
Class OJI.i. 



Book. 



^ 5? 



GopyiightN^. 



Ci}E3a{IGKT DEPOSIT. 



DISEASES OF ECONOMIC PLANTS 



THE MACMILLAN COMPANY 

NEW YORK • BOSTON • CHICAGO • DALLAS 
ATLANTA • SAN FRANCISCO 

MACMILLAN & CO., Limited 

LONDON • BOMBAY ■ CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA. Ltd. 

TORONTO 



DISEASES 



OF 



ECONOMIC PLANTS 




^ BY 



f/l/^STEVENS, Ph.D. 

PROFESSOR OF PLANT PATHOLOGY IN THE UNIVERSITY 
OF ILLINOIS 

AND 

J. G. HALL, M.A. 

FORMERLY ASSISTANT IN VEGETABLE PATHOLOGY IN THE 
NORTH CAROLINA AGRICULTURAL EXPERIMENT STATION 



REVISED EDITION BY F. L. STEVENS 



THE MACMILLAN COMPANY 
1921 

All rights reserved 



§13731 



OoPYBiQHT, 1910 and 1921,* , 
By the MACMILLAN COMPA-NY. 



Set up and electrotyped. Published September, 1910. 



Revised Edition, January, 1921. 



JAN 19192! 

« 

©CU605427 



PREFACE 

The present edition of this text-book is designed primarily 
for college students, but it is hoped that it may serve also 
as a useful handbook for others who may wish to recognize 
plant diseases or to apply treatments. It aims to give a 
comprehensive view of the field and its importance, with 
diagnostic symptoms and suggested treatment of all of the 
more important diseases prevalent on the crop plants of the 
continental United States with brief notes or mere mention 
of those less serious. A few of the more important diseases 
not of the United States are also discussed briefly. Diag- 
nostic characters are limited in the descriptions to those that 
may be recognized without the aid of the microscope. For 
further discussion of morbid histology, or of the morphology 
of the parasites concerned, the reader is referred to other 
books on these subjects. Descriptions and discussions of 
treatment are as full as the space admits and the reader who 
desires more complete information is referred to the pertinent 
literature cited. 

Since conditions are so diverse as to geographic loca- 
tion, climate, and soils the treatment here suggested must 
be more or less general. Crop growers should in all cases 
endeavor to secure from the nearest Agricultural Experi- 
ment Station the information best applicable to local con- 
ditions. 

The segregation of certain diseases under the caption 
''Minor diseases" is arbitrary and it is quite possible that 
diseases here included may locally or seasonally be of major 
importance, and conversely that certain major diseases may 
be of but minor importance. The aim, however, is to in- 
dicate to the student those which in general are less wide- 
spread or less likely to be serious. Ample cross references are 



vi Preface 

given to render tlie information more accessible and to avoid 
repetition. 

The common names selected are those that are in general 
use. 

Diseases due to insects comprise a group which involves 
knowledge of the classification of insects and of their life- 
habits. Such diseases are set aside in the special field of 
the Entomologist and are not here treated. The diseases 
due to adverse inanimate environmental conditions, the 
sickening of plants due to lack of soil fertility, to excess of 
some element, to overabundance or lack of water or to im- 
proper physical condition of soil, etc., are recognized as 
properly belonging in the field of Agronomy and are treated 
in this book only in exceptional cases. 

During the decade that has elapsed since the publica- 
tion of the first edition there have come into prominence 
in the United States numerous diseases at that time un- 
known in America. Therefore the present edition includes 
discussion of several scores of diseases of major importance, 
some of minor importance, as well as many modifications of 
treatment that did not appear in the earlier edition. 

The author desires to express his especial thanks for 
aid in the preparation of this volume as follows: To R. 
J. Haskell of the Plant Disease Survey of the U. S. Depart- 
ment of Agriculture, who has kindly read the proof with 
particular reference to the usage of common and scientific 
names and as to the estimates of losses and statements 
regarding geographic distribution; to H. W. Anderson of 
the University of Illinois for valuable aid in the preparatiofi 
of the sections treating of fruit disease; to E. C. Stakman 
of the University of Minnesota in connection with the cereal 
diseases; to G. L. Peltier of the Alabama Experiment 
Station and W. A. Ruth of the University of Illinois for the 
preparation of special articles. 

F. L. Stevens. 

Urbana, Illinois, 
August, 1920. 



CONTENTS 



Historical ...... 

Damage Caused by Plant Diseases 

Prevention or Cure of Plant Diseases 
Methods of Prevention 



General Diseases 

Diseases of Special Crops 

Pomaceous Fruits . 

Drupaceous Fruits . 

Small Fruits . 

Tropical Fruits 

Vegetable and Field Crops 

Cereals .... 
Cereal Smuts in General 
Cereal Rusts in General 
Anthracnose of Cereals 
Special Diseases of Cereals 

Forage Crops . 

Fiber Plants . 

Trees and Timber . 
General Diseases 
Special Hosts . 

Ornamental Plants . 
General Diseases 
Special Diseases 

Fungicides . . 

Spraying Apparatus 

Soil Disinfection 

Bibliography 

Index .... 



vu 



page 
1 

10 

13 
14 

19 

31 
31 
74 
102 
135 
149 
266 
266 
275 
280 
280 
321 
343 
354 
354 
381 
406 
407 
408 

440 

452 

460 
467 
491 



DISEASES OF ECONOMIC PLANTS 



DISEASES OF ECONOMIC 
PLANTS 



HISTORICAL 



1, 2, 26, 27 



The science of Plant Disease or Phytopathology was ir 
its early formative period between 1853 and 1870, the 
foundations being laid in the pioneer work of Berkeley, 
De Bary and the Tiilasne brothers in establishing the 
parasitism of the fungi, and in Pasteur's fundamental work 
on Bacteria and Spontaneous Generation. 

To be sure some of the most conspicuous diseases had 
long been known by sight. Blight and mildew were re- 
ferred to in both the Old and the New Testament. Wheat 
rust was mentioned by Aristotle, 350 B.C. and reference 
to mildew is found in King Lear, Act III, Sc. 4. There 
was legislation even regarding wheat rust as early as 1660. 
However, there was little or no real knowledge of plant 
diseases in those times, beyond the fact that various diseases 
existed, and this knowledge was shrouded in superstition. 

Following the pioneer publications of Berkeley, De Bary, 
and the Tulasne brothers came the more complete treatises 
of Kuehn (1858), Hartig (1874), Frank (1880, 1895), Sorauer 
(1874, 1886, 1908), Kirchner (1890), Tubeuf (1894), Prillieux 
(1895), Delacroix (1902, 1908, 1911), Ward (1896, 1901, 
1909), and others. 

It was not until 1873 that plant pathology became a 
part of instruction in botany, and not until 1875 that special 
courses in pathology were given in any of the schools of 
America. 

A series of papers begun by Burrill in 1873, another by 
Farlow in 1875, and other publications by Bessey, con- 

1 



Diseases of Economic Plants 





T. J. Burrill, 1839-1916 



B. D. Halsted, 1852-1916 





C. E. Bessey, 1845-1915 



G. F. Atkinson, 1854-1918 



Historical 3 

tributed to the knowledge of plant disease and served 
especially to awaken interest in the problems of, and to at- 
tract students to, this field of research. 

In 1879 Burrill, working upon the blight of the pear and 
apple, was the first to attribute a plant disease to bacterial 
origin. His work was confirmed and his conclusions more 
fully established by Arthur. 

During the seventies, from two or three workers in this 
field, the number rapidly grew, augmented in the middle 
eighties by the introduction of plant pathology into the 
Agricultural Experiment Stations and the United States 
Department of Agriculture, until the number of papers 
published in the United States upon plant pathology be- 
tween 1888 and 1900 is estimated at over four thousand. 
While only a few dozen plant diseases had been even cursorily 
described in the United States prior to 1880, in 1910 a total 
of some 525 diseases, of which more than 250 were serious, 
had been carefully investigated and the number since that 
date has been greatly increased. 

Historical concerning plant-disease prevention.^' ^^^ 
Though little could be done to devise rational methods of 
combating plant diseases until their causes were known, a 
very few rule-of -thumb, empirical ways of meeting them 
had been suggested in very early days. As might be ex- 
pected, many of the methods used were valueless. Thus 
Parkinson early in the seventeenth century advocated the 
use of vinegar to prevent canker on trees, and Forsyth in 
1790 gave the following directions for making a mixture to 
''cure disease, defects, and injuries of plants."^ ''Take one 
bushel fresh cow dung, one half bushel lime rubbish from 
old buildings, one half bushel wood ashes, one sixteenth 
bushel pit or river sand. The last three are to be sifted fine 
before they are mixed. Then work them well together with 
a spade, and afterward with a wooden beater until the stuff 
is very smooth, like fine plaster used for the ceilings of rooms." 
Soapsuds or urine was used to make the composition of the 
consistency of plaster or paint. After being applied it was 



4 Diseases of Economic Plants 

covered with a sifting of powder made of "dry powder of 
wood ashes, mixed with the sixth part of the same quantity 
of the ashes of burnt bones." 




Fig. 1. — Erwin F. Smith of the United States Department of 

Agriculture. 

Among the early chaff, however, there were some grains 
of wheat. Thus Riedel in 1751 advised excision followed by 
grafting wax for canker, and Robertson in 1821 said: ''Sulfur 
is the only specific remedy that can be named for the treat- 



Historical 5 

ment of mildew on peaches. It should be mixed with soap- 
suds and then applied by dashing it violently against the 
trees by means of a rose syringe;" thus advocating a rem- 
edy which, modified, is still prominent for this class of 
diseases. 

The aggressiveness of several plant diseases in Europe 
between 1878 and 1882, particular^ the downy-mildew 
upon the grape, which, about 1878, had invaded Europe 




Fig. 2. — Millardet, 1838-1902, father of the 
Bordeaux mixture. Professor at the Univer- 
sity of Bordeaux. 

from America, stimulated a search in the former country 
for effective spraying mixtures. Trials of many chemicals 
were made, but it was left to accident to suggest, and to 
the genius of Millardet, of Bordeaux, France, to perfect, 
the happy combination of lime and bluestone that we now 
know as Bordeaux mixture. It was customary in certain 
vineyards to sprinkle a few rows of grapevines near the 
road with a mixture of milk of Kme and bluestone to give 



6 Diseases of Economic Plants 

them a poisonous appearance to ward off depredation of 
the hungry passer-by. The vines so treated in 1882 were 
noted by Prillieux and Millardet to be less injured by 
the mildew than were other vines, and they ascribed the 
beneficial effect to its proper cause, the Hme-bluestone 
mixture. 

While several investigators were engaged simultaneously 
in experimenting with these chemicals upon the mildew, 
it was Millardet who first planned and executed experi- 
ments and published results which demonstrated the com- 
mercial value of the lime-bluest one treatment. 

The first systematic applications of copper, and of copper 
with lime as a disease preventive, were made under the 
direction of Millardet, August 18, 1883. In 1884 the work 
was repeated, and in 1885 Millardet published the first 
directions for preparing Bordeaux mixture : 

Water . .... 130 liters (34 gallons) 

Bluestone ..... 8 kilograms (17.6 pounds) 
Lime ..... 15 kilograms (33 pounds) 

This mixture was to be shaken upon the plants with a 
broom. 

Following this demonstration came the introduction of 
an era, not yet at an end, of active experimentation with 
fungicides, wet and dry, which has already yielded results 
of incalculable value. 

In 1885 also appeared for the first time the Ammoniacal 
Copper Carbonate proposed b}^ Professor Audoynaud of 
the Montpelier Agricultural School. 

Saunders, in the Canadian Horticulturist in 1884, sug- 
gested the use of several liquid spraying mixtures for apple 
scab, but little if any liquid spraying for plant diseases" was 
done in America prior to 1885. 

In 1885, from the Section of Mycology, Division of Bot- 
any, United States Department of Agriculture, appeared an 
article by Lamson-Scribner, giving directions for making 
"the copper mixture of Gironde," the primitive Bordeaux 



Historical 



mixture. In 1886 the spraying campaign may be said to 
have been well started in this country. 

The disinfection of seeds by bluestone was practiced first 
with the cereals as early as 1807 by Prevost of France, and 
improved by Dreisch in 1873, by the addition of a limewater 
bath to follow the bluestone. In 1887 Jensen of Denmark 
improved upon these methods by developing his hot-water 
treatment, which has since proved 
of great value, not so much for its 
primary use, in which it has been 
superseded by formalin, but owing to 
its applicability to those loose smuts 
which cannot be successfully treated 
by surface disinfection. Similar seed 
treatments have been extended to 
the potato by Bolley, and to cabbage 
by Harding. 

The production, by breeding, of 
new and disease-resistant varieties is 
one of the latest and most promising 
methods of combating plant diseases. 
Grapes resistant to Phylloxera were 
produced by Millardet; cotton, cow- 
peas, and watermelons resistant to 
wilt by Orton; cabbage by Jones; 
tomato by Durst and others; tobacco 
resistant to Thielavia by Johnson. 

No small part in the progress that 
has been made in the prevention of 
plant disease is due to the improve- 
ment of appliances, dusters, pumps, nozzles, etc., for dis- 
tributing the disinfectants upon the plants. This progress is 
well illustrated by comparing the broom of Millardet with 
the knapsack, barrel, or power sprayer of to-day. 




Fig. 3. — An improved 
brush for distributing 
Bordeaux mixture. 
After Lodeman. 



8 Diseases of Economic Plants 

Important Events in Plant Disease History 

Ancient, Recognition of the existence of plant diseases in early 

Biblical times. 
1683 The discovery of bacteria. Loewenhoek. 
1807 The efficiency of copper against smut spores discussed. 

Prevost. 
1821 The use of sulfur as a fungicide recommended. Robertson. 

1845 The use of boiled sulfur and lime for mildew advocated. 

1846 The studies of Rev. M. J. Berkeley. 

1853 The beginning of the ''Morphology and Physiology of the 

Fungi" and the proof of parasitism of fungi. De Bary. 
1861 The publication of the first American paper on plant pathology. 

Engelmann. 
1860-1864 The founding of bacteriology. Pasteur. 
1864 The proof of alternation of hosts, heteroecism. De Bary. 
1869 The first university publication in America regarding plant 

pathology. University of Illinois. 
1873 Plant pathology taught incidentally with botany in America. 

Burrill. 
1875 Plant pathology first taught as a special subject in America. 

Farlow. 
1879-1880 Proof of bacterial disease in plants. Burrill. 
1880 The discovery of the cyclone principle in nozzles. Barnard. 
1882 The beginning of "Sylloge Fungorum." Saccardo. 

1884 Systematic introduction of plant pathology into American 

Agricultural Experiment Station work. Arthur. 

1885 The announcement of the Bordeaux mixture. Millardet. 

1885 Organization of a Section of Mycology in the Division of 

Botany, United States Department of Agriculture. Lam- 
son-Scribner. 

1886 Proof that mosaic is infectious. Mayer, 

1887 The hot-water treatment for smut. Jensen. 

1888 The introduction of formalin as a disinfectant. Trillat. 
1888 Organization of the State Agricultural Experiment Stations. 
1890 The beginning of pump improvement for spraying. 

1894 Establishment of the fact that biologic races exist. Eriksson. 



Historical 9 

1906 The passage by Congress of the Adams Act. 

1906 The introduction of the use of Hme-sulfur. Cordley. 

1907 EstabHshment of the first university department of plant 

pathology. Cornell. 
1909 The organization of the American Phytopathological Society. 
1912 The passage by Congress of the Plant Quarantine act. 



DAMAGE CAUSED BY PLANT DISEASES 

The crop grower often suffers much damage from plant 
diseases, entirely unconscious of the fact that his crop is 
affected by disease. Or, if the presence of disease is recog- 
nized, the amount of damage is often underestimated. Thus 
the presence of oat smut to the extent of 15 or even 40 per 
cent, is sometimes entirely overlooked by an otherwise ob- 
servant man. 

An attitude of willful disbelief in the prevalence of a 
disease is often couched in such terms as these: "I don't 
see why I must work to protect my apples from rot. My 
grandfather used to raise fine apples without any attention 
to these things." 

It must be recognized that plant diseases are with us; 
that they are increasing by importation from other coun- 
tries or other states; that diseases formerly insignificant 
are, in many instances, becoming serious; that long, inten- 
sive culture of one crop in a locality permits new diseases 
to develop. Diseases have many means of dispersal; on 
seed, hay, or other produce shipped by mail, express, or 
freight; on animals; by wind; by water; by birds. Diseases 
will continue to spread and to increase in destructiveness 
until the individual and the general public are aroused to 
such active appreciation that conditions of plant sanitation 
and plant protection become much more general and effective 
than they now are. 

Conspicuous examples of the advent of diseases in coun- 
tries where they were before unknown, are afforded by the 
following: grape powdery-mildew, native to America and 
first seen in Europe in 1845; the American gooseberry mildew, 
first found in Europe in 1900; the potato late-blight, native 
to South America, noted in Europe in 1830; the asparagus 
rust, introduced from Europe about 1896; the hollyhock 

10 



Damage Caused by Plant Diseases 11 

rust introduced about 1886; the white-pine bhster-rust 
introduced from Germany shortly prior to 1906; the chestnut 
bark-disease, introduced from the Orient about 1904. Other 
examples are cabbage club-root, potato-wart, grape an- 
thracnose, grape black-rofc, the carnation rust, and citrus 
canker. 

Cases of interstate migration of plant diseases are numer- 
ous, ^^^ most prominent being, perhaps, the asparagus, holly- 
hock, carnation, and chrysanthemum rusts, and the pear- 
blight. 

Fungi introduced into new environment, into a new con- 
tinent, for example, owing to the change in biologic equilib- 
rium, to the absence, perhaps, of their natural enemies or to 
readier access to susceptible hosts are often much more de- 
structive than in the countries from which they came. This 
fact finds illustration in many of the diseases mentioned 
above, notably so in the case of the chestnut bark-disease. 

Aside from diminishing the value of the produce and the 
thrift and future productiveness of perennials, as trees, 
vines, etc., plant diseases entail depreciation in the value 
of land, and in some cases even occasion large loss of life. 
Thus the famine in Ireland in 1845 is directly traceable to 
the injury done to the potato crop by the potato late-blight. 
The presence of ergot in grain used as food for cattle or man 
results in disease and death. 

The presence in land of the causal germ of the melon, 
cowpea, cotton or tobacco wilts, of onion smut, cabbage 
club-root or black-rot, or of any one of many other soil-borne 
pathogenes precludes the possibility of successful culture 
of the susceptible plant for a long period of years, perhaps 
forever, upon the soil in question. Such restriction may 
prevent the raising of the crops that are most profitable 
in a particular section, and in some instances depreciation 
of 50 per cent or more in the market value of land has resulted 
from the invasion of one of these ineradicable soil pests. 
Still more serious is this kind of injury if the crop in ques- 
tion is one which requires large money outlay before the 



12 Diseases of Eco7iomic Plants 

presence of the disease germs is manifest. In the case of 
Sumatra tobacco under shade, or lettuce grown under 
canvas, the money expended to prepare for the crop may 
aggregate from $700 to $1000 or even more per acre the 
first year. The capture of such acreage by the lettuce 
drop or the tobacco wilt is a far more serious matter than 
a plant disease is usually considered to be. 

The diseases which develop on the product after harvest, 
while in storage, are of peculiar destructiveness since they 
cause the loss of a large percentage of the finished agricul- 
tural yield. ^' ^ Thus a large part of the total yield of sweet 
potatoes is lost. Those diseases that develop in transit entail, 
in addition to the loss of the product, also the freight charges 
and many hundreds of thousands of dollars in litigation. 

Some of the losses caused by diseases of a few crops are 
given below, merely as illustrative instances. The authority 
is named with each estimate. These losses are in many 
instances much larger than is indicated, due to increase in 
market value of the product. 

The California vine disease in 1892, $10,000,000. Pierce. 

Wheat rust in the United States, 1898, $67,000,000. Galloway. 

Wheat rust in Illinois, 1885, $1,875,000. Burrill. 

Violet leaf-spot in the United States, 1900, $200,000. Dorsett. 

Peach leaf-curl in the United States, 1900, $2,335,000. Pierce. 

Potato late-blight in New York, 1904, $10,000,000. Stewart. 

Oat smut in the United States, annual, $6,500,000. Orton. 

Wheat loose smut, United States, annual, $3,000,000. Orton. 

Wheat bunt in the United States, annual, $11, 000,000. Orton. 

Potato blight in the United States, annual, $36,000,000. Orton. 

Wheat, 1917, all diseases, 64,440,000 bu. Lyman.« 

Oats, 1917, all diseases, 153,973,000 bu. Lyman. 

Corn, 1917, all diseases, 175,344,000 bu. Lyman. 

Potato, 1917, all diseases, 117,174,000 bu. Lyman. 

Sweet potato, 1917, all diseases, 41,707,000 bu. Lyman. 

Cotton, 1917, all diseases, 1,866,000 bales. Lyman. 



PREVENTION OR CURE OF PLANT DISEASES 

The burden of the efforts of the plant pathologist must 
be directed toward methods of prevention, which are 
here worth far more than their proverbial ratio, since, 
owing to the comparatively small value of the individ- 
ual among plants, treatment of a plant already sick is 
seldom attempted except in the case of plants of ex- 
ceptional value. Such value very rarely attaches to an- 
nuals or biennials; hence it is only with perennials, 
valuable vines, bushes, or trees that cure of the in- 
dividual is attempted, and here only in a few special 
cases. 

The science of plant pathology, barely antedating 1880, 
is yet young. Several of its founders in America are living 
and are still vigorous workers. In comparing this youthful 
science with its far more aged prototypes, human and vet- 
erinary medicine, one is astonished at the progress already 
made, rather than abashed at the multitude of diseases as 
yet unconquered.'^^ 

Among all classes of crops are diseases, single or many, 
which have given way to the control of man, many of them 
diseases of great destructiveness, yet which are now prac- 
tically under the subjugation of the intelligent, educated 
crop producer. 

The remedies, with one or two exceptions, are entirely 
the result of patient, scholarly investigation, careful de- 
duction, followed by experimenting, testing, and improving. 
Such investigation is ever proceeding with increasing ac- 
tivit}^, and each year, new or improved methods of combat 
are devised, so that the future may with confidence be 
relied upon to see the subjugation of many of the foes that 
are as yet un conquered. 

13 



14 Diseases of Economic Plants 

Methods of Prevention 

All methods of prevention of plant diseases due to par- 
asites aim at the destruction of the causal organism, the 
diminution of its numbers, or the strengthening of the crop 
plant so as to withstand its attack. The various methods 
employed may, for convenience, be summarized as follows : — 

1. Killing the causal organism as it rests upon the seed. 
— Examples: oat or wheat smut, cabbage black-rot. For 
this purpose the seeds (sometimes cuttings or even whole 
plants are similarly treated) are subjected to the action of 
heat or disinfecting chemicals long enough to kill the causal 
organism, but not long enough to kill the seeds. Chief 
among such disinfectants are : — 

Formalin (40 per cent formaldehyde). 

Corrosive sublimate. 

Copper sulfate, followed by weak limewater. 

Heat. 

2. Killing superficial fungi by applications upon the 
green parts of the plant. — Examples: powdery-mildew 
upon grape, gooseberry, or rose. This method is applicable 
only with the purely superficial fungi, since internal para- 
sites cannot be so reached without injury to the host plant 
itself. It finds prominent application with the powdery- 
mildews. The chief applications used are : — 

Liver of sulfur. 
Bordeaux mixture. 
Ammoniacal copper carbonate. 
Sulfur, or sulfur and lead arsenate. 
Lime-sulfur. 

3. Killing superficial fungi hibernating upon the bark of 
the dormant plant or plant supports. — Examples: apple 
hypochnose, peach curl. For this purpose cleansing sprays, 
often called dormant sprays, may be used. Since the parts 
of the host receiving the spray are highly resistant to their 
poisonous action, the sprays thus employed may be much 



Prevention or Cure of Plant Diseases 15 

stronger than could safely be used when the plant is in 
foliage. For this purpose use : — 

Copper sulfate with lime sufficient to color. 
Lime-sulfur mixtures. 

4. The use of protective sprays or dusts. — Examples: 
grape black-rot, apple scab. A protective spray or dust is one 
applied to the plant upon its bark, foKage, or fruit, to kill 
any offensive germs that may fall upon its surface, or to pre- 
vent their growth upon or into the plant. Such sprays are 
distinguished from the cleansing sprays, which are not 
primarily for protection against future invasion, but rather 
for the purpose of cleaning off or killing all spores actually 
upon the plant. Protective applications are usually em- 
ployed when the plant is in foliage, and therefore must be 
used with due regard to the susceptibiHty of the plant to 
the poison employed. They should be applied : — 

1. Often enough to replace any previous protective ap- 
plications that may have been removed by rain or other 
means. 

2. To give protection to any new surface of twig, leaf, 
or fruit which has developed since the last protective treat- 
ment was made. 

The first protective application should be given as soon as 
possible after susceptible surfaces have developed, and 
before the attacking organisms are expected to make their 
invasion. The time varies of course with each special crop, 
with each disease, with the climatic relations and section 
of the country. Nor can any absolute rule be laid down 
for the use of subsequent protective applications. Fre- 
quency of rain is an important controlling factorr A fungi- 
cide, if rained upon just after it is applied and before it has 
time to dry, is easily washed off. 

New tissue and new surfaces develop every day; there- 
fore, theoretically to secure complete protection, sprayings 
should be very frequent, much more frequent than is prac- 
ticable. To meet the needs occasioned by new growth, pro- 



16 Diseases of Economic Plants 

tective sprays are usually given at intervals of from ten to 
fourteen days, though special rules must govern special cases. 

The chief protective applications are : — 

Bordeaux mixture, full strength or weak. 

Ammoniacal copper carbonate. 

The latter solution possesses the advantage that it does 
not spot the fruit and may therefore be used near the period 
of maturity, when the Bordeaux mixture, owing to its 
spotting effect, would be less desirable. 

Lime-sulfur mixtures. 
Sulfur and lead arsenate. 

5. Excision of the affected parts. — Examples: Ash 
white-rot. Excision is resorted to chiefly in the case of trees 
which from their location or quality possess value suffi- 
cient to warrant the necessary outlay of labor. It is so 
practiced as to remove the diseased wood and sufficient of 
the healthy wood to expose an entirely un contaminated sur- 
face. The wounded surface is then treated with an antiseptic 
such as tar or carbolineum. 

6. Removal and destruction of diseased twigs, leaves, 
or fruit. — Examples: fire-blight, peach brown-rot. The 
removal and destruction of diseased parts diminishes the 
number of bacteria, spores, etc., that are available to spread 
the disease and thus lessens infection. Mummified fruit 
should be picked from the plant or the ground and destroyed, 
or it may be removed by appropriate pasturage by fowls, 
swine, etc. Affected leaves in many instances should be 
similarly removed. Blighted twigs and cankers should be 
cut out when seen. 

7. Removal, in whole or in part, of complementary hosts. 
— Examples: apple rust, wheat rust. Complementary hosts 
always serve as multiplying places for the causal parasite, 
and in some instances are absolutely essential to its hiberna- 
tion. Such complementary hosts should, when practicable, 
be removed from the immediate vicinity, and, when possible, 
not allowed to exist within considerable distance, one eighth 



Prevention or Cure of Plant Diseases 17 

to one half mile, or better still, a greater distance. When 
it is not practicable to remove the host, the offending por- 
tions may be cut away, e. g. in the case of the apple rust 
the cedar-l)alls may be removed from adjacent trees. 

8. Avoidance of disease-bearing material or material 
favoring disease. — Infection may reach hay through sick 
melon vines (melon wilt), or manure may be contaminated 
by infected plant parts (potato scab, cal:)bage rot, melon 
wilt, etc.). Soil may wash from one field to another and bear 
disease with it (tobacco wilt, melon wilt, etc.). 

9. Prevention of wound infection. — Excnnples: heart- 
rots, sap-rots, cankers, fruit-rots. Wound infection may 
often be avoided by care in handling the plant so as not 
to wound it. In trees place ladders carefully, not roughly, 
among the limbs; avoid walking on limbs with nailed or 
hard boots, etc. Gather all fruit, root-crops, etc., carefully 
to avoid breaking the skin or bruising the underlying tissue. 
In case of removal of large limbs, coat the exposed wood 
with paint or tar to prevent invasion by parasites. 

10. Avoidance of susceptible varieties ; selection of resist- 
ant varieties. — There is much difference in the suscepti- 
bility of different varieties of plants. Study the different 
varieties of the crop to be raised, particularly in this regard, 
and use those that are most resistant. In case resistant 
individuals are observed among sick plants, save their seed 
carefully and test the resistance in succeeding years. In 
this way new and resistant varieties may be developed. 

11. Avoidance of disease-infested localities. — This is in 
many cases imperative where the soil is invaded by a germ 
inimical to the growth of crops of certain kinds, as in the case 
of cabbage black-rot, cotton and melon wilt, etc. Similarly, 
low damp locations favor diseases of some crops (potato late- 
blight) , and the proximity of certain kinds of plants leads to 
disease with others (apple rust). All this should be con- 
sidered in the selection of land for the crop. 

12. The practice of crop rotation. — Constant growth 
of the same crop in any locality tends to increase the enemies 



18 Diseases of Economic Plants 

of that crop. Rotation breaks the continuity and hinders 
the multipHcation of the parasite. 

13. Avoidance of practices that aid in dissemination of 
the parasite. — Examples: bean pod-spot, tomato leaf -spot. 
In certain instances the spore of the causal fungus is trans- 
ferred from plant to plant most freely when the host is wet. 
To avoid picking or cultivating under such conditions is to 
lessen the spread of infection. Similarly in the greenhouse, 
surface watering may spread the spores. By sub-irrigation 
this may be avoided. 

The importance of sanitary methods cannot be over- 
emphasized and stress on such methods rather than on the 
employment of specific treatment against disease is a growing 
tendency. Many crops from their very nature are but 
slightly amenable to direct treatment; others will not need 
it if they are given surroundings that are, in general, sanitary. 
Increased attention should, therefore, be given to soil condi- 
tion both chemical and physical, to the fitness of the crop to 
the particular soil and climate, to water relations, to crop 
rotation, to closeness of planting, ventilation, to proper seed 
selection, and modes of propagation. 



GENERAL DISEASES 

The diseases discussed below are present upon so many 
different species of plants that it would seem that they are 
almost indifferent to the nature of their hosts. They may, 
therefore, be expected upon any kind of plant, and are here 
mentioned so that it will not be necessary to discuss them 
repeatedly in succeeding pages. Special reference is also 
made to them under the hosts upon which they are most 
destructive. 

Damping-off. ^^' ^^' ^^ — SeedUngs, cuttings, and other 
weak, soft plants which lack in the vigor that affords them 
natural protection against their enemies, are subject to a 
disease which has come to be generally known to gardeners as 
'^ damping-off." Damping-off is most injurious to seedlings 
grown indoors or under crowded conditions, but it some- 
times occurs in the field. It is particularly injurious to 
seedling trees in the nursery where many young seedlings die 
and disappear, or even die before they come above ground. 
The loss is thus often 90 per cent of the stand. Typically 
damping-off occurs upon seedlings as a rot originating at or 
near the surface of the ground. The decay at this point so 
weakens the stem that the plant topples over or ''damps- 
off." Subsequently the whole plant may decay, either 
from the primary cause or from secondary attacks. A short 
time prior to the fall of the plant the leaves may appear 
sickly, although this sign is so evanescent that it may not be 
noted. 

Upon cuttings the toppling over does not, of course, occur, 
but the rot at the ground line is of the same nature as in 
the case of seedlings, and since the diseases in the two cases 
are of similar nature and due to similar causes, they are 
placed under the same caption. 

Damping-off may be caused by any one of several species 

19 



20 



Diseases of Economic Plants 



of fungi, prominent among them being Pythium, Thielavia, 
Corticium, Fusarium, Botrytis, Sclerotinia, Sclerotium, 
Phoma, Volutella, Phytophthora, CoUetotrichum, Gloeospo- 




FiG. 4. — Stems of young greenhouse tomato plants damped- 
off frcm attacks of Corticium. After Humbert. 



rium. The fungus which causes this condition ma}^ often be 
seen as a weft of myceHum around the base of the diseased 
plant, or even creeping over the ground to some distance. 



General Diseases 21 

From its original points of attack it may spread rapidly to 
adjacent plants, often sweeping the whole seed bed. 

Since the growth of these fungi is favored by moisture 
and warmth, the trouble may often be checked or pre- 
vented by keeping the beds cool and withholding any excess 
of water; also by means of adequate ventilation, preventing 
the accumulation of a vapor-laden atmosphere around the 
bases of the plants. Thick sowing should be avoided. 
Frequent stirring of the top soil around the plants aids in 
drying it and may stop an incipient attack of damping-off. 
Organic matter in the soil favors the growth of damping- 
off fungi, and should be avoided. Fresh, clean sand is best 
for most purposes of the seed bed and cutting bench. 

Soil known once to have sustained damping-off may be 
regarded as infested with the fungus which caused it. Such 
soils should not be used for seedlings or cuttings without 
disinfection. If disinfection is impracticable, the soil should 
be removed, the containers thoroughly cleansed with a 
spray of Bordeaux, bluestone, or formalin, and new unin- 
fested soil introduced or, in the case of seed beds, a new site 
selected. 

Stem-rot, Root-rot ^^' ^^ {Cortidum vagum B. & C, Rhizoc- 
tonia). — The affected plants are usually attacked near the 
soil-line or on the roots where cankers of small or large extent 
develop. These cankers vary in character and color with the 
host and conditions so that reliable diagnosis can be made 
only by recognition of the fungus with a compound micro- 
scope. There appear very fine, cobwebby threads, pale or 
dark, which are often barely visible around the roots of the 
affected plants as they are pulled from the ground. Masses 
of fungus threads (sclerotia), also often occur. These are 
black, irregular in shape, the size of a pin-head or larger. 
Usually the fungus does not bear spores, but in relatively 
rare instances sporiferous regions develop encircling the 
stem. 

This stem-rot has long been known in Europe, and is now 
found in North and South America, the West Indies, India, 



22 



Diseases of Economic Plants 




Fig. 5. — Corticium on cabbage. 
Peltier. 



cherry, 
ble to 



raspberry, 
its attack 



and Australia, and may 
be regarded as of world- 
wide distribution. The 
first account of it in 
the United States was 
made by Pammel in 
1891. Since then nu- 
merous bulletins deal- 
ing with it on various 
hosts have been pub- 
lished. It is quite in- 
different to its hosts, 
embracing especially 
members of the pink, 
crucifer, legume, po- 
tato, and sunflower 
families and in all about 
fifty families of plants 
including conifers and 
ferns. Some 165 spe- 
cies and varieties of 
host plants are re- 
corded. Among these, 
the most important in 
America are : potato, 
beet, lettuce, bean, cel- 
ery, carrot, cabbage, 
eggplant, tomato, 
sweet potato, cucum- 
ber, watermelon, pump- 
kin, squash, pea, corn, 
radish, rhubarb, alfalfa, 
clover, buckwheat, to- 
bacco, cotton, aster, 
carnation, violet, 
currant, pine. If conditions favora- 
obtain, the fungus may well be ex- 



After 



General Diseases 23 

pected upon almost any species of plant, so wide is its range 
of hosts. 

Soil disinfection (p. 460), when practicable, may be em- 
ployed; otherwise general sanitary measures, destruction of 
infective refuse, and the use of resistant plants are remedial. 

Southern-blight^'^ (Sderotium rolfsii Sacc). — Plants af- 
fected with this disease lose color, wilt, and may die. The 
fungus is found, usually, around the base of the stem or on 
the roots, producing lesions of rot, a dense white mycelial 
mat, and large numbers of spherical, yellow sclerotia, closely 
resembling mustard seeds, which are diagnostic. The causal 
fungus may be recognized upon numerous hosts particularly 
in the Southern states, and as far north, at least, as central 
lUinois. It has been identified upon tomato, eggplant, Irish 
potato, sweet potato, beet, peanut, pepper, cauliflower, 
bean, cowpea, cabbage, carrot, squash, muskmelon, water- 
melon, rhubarb, fig, cotton, violet, hydrangea, daphne, 
chrysanthemum, pinks, bellflower, morning-glory, Japanese 
fiber-plant, grasses, sugar cane, and several weeds and may 
be looked for on any plant. Treatment is the same as for 
stem-rot. 

Texas root-rot ^^' ^'^ (Ozonium omnivorum Sh.).* — Most 
destructive to cotton (see p. 346) this disease affects a very 
wide range of plants in Texas, California, Oklahoma, New 
Mexico, and Arizona. It has been noted upon nursery 
stock, apple, mulberry, chinaberry, linden, ash, quince, locust, 
Prunus, hibiscus, persimmon, elm, lime, maple, beet, peanut, 
bean and various legumes, flax, cotton, sweet potato, Sida, 
ragweed, cocklebur, alfalfa, and several other plants. The 
chief characteristics are a sudden wilting or dying of the 
diseased plant, or if the main root is not completely diseased 
merely a slight yellowing and unhealihy appearance. The 
roots of plants that have recently died are closely invested 
with a cinnamon-buff felt of hyphse, in which strands are 
conspicuous. Treatment is as for stem-rot. 

* Duggar believes the conidial stage to be Phymaioirichum omnivorum 
(Sh.) Dug.i7 



24 Diseases of Economic Plants 

Root-rot 1^' 1^ {Thielavia basicola (B. & Br.) Zopf.).— 
The roots of the diseased plants, especially the tips of the 
rootlets, turn black and decay. Sometimes the stem just 
above the roots is cracked and deformed and the plant is 
dwarfed. Damping-off may occur in seed beds. This root- 
rot was first noted in the United States on tobacco in 1904 
and is now known to be widely distributed. It is found pri- 
marily on members of the legume, potato, and cucurbit 
families but has been identified on plants of fifteen other 
families as well, including the violet, composite, crucifer, and 
mallow families. In all, something over a hundred species 
of host plants are known to be susceptible, though to largely 
differing degrees. In the case of tobacco alone the average 
annual loss is placed at millions of dollars. There appears 
to be no biologic specialization and the fungus that can affect 
one crop can pass readily to the others. For treatment, see 
under Tobacco, page 253. 

Root-knot, nematode galls.- ^' ^^' ^^ — Root galls, varying 
from a few millimeters to a centimeter or more in size and 
superficially resembling the root tubercles of the legumes, 
are common upon a large variety of crops, causing large 
field loss in all but the most northern states as well as serious 
injury in greenhouses everywhere. Plants badly affected 
are dwarfed and are more susceptible to attacks of fungi 
than are normal healthy plants. Large indirect loss arises 
from the fact that nematode-infested soil often prohibits the 
planting of certain profitable crops. These galls are due to a 
microscopic eel-worm (nematode) which enters the root 
from the soil and by irritation of the root causes the gall to 
develop. Following is a list of the more important highly 
susceptible plants. A complete list would number over five 
hundred hosts. Field crops: alfalfa, clover, cotton, cowpea 
(except Iron, Brabham, and hybrids of Whippoorwill crossed 
on Iron), field pea, flax, pumpkin, soy bean, sugar beet, 
sugar cane, sweet potato, tobacco, vetch. Ornamental and 
drug plants: begonia, cineraria, clematis, coleus, dahlia, 
hollyhock, ginseng, goldenseal, peony, rose, sweet pea, violet. 



General Diseases 



25 



Truck crops: asparagus, bean, carrot, celery, cucumber, 
eggplant, garden beet, garden pea, Irish potato, lettuce, 
muskmelon, okra, onion, pepper, salsify, spinach, straw- 
berry, tomato. Woody plants: almond, catalpa, cherry, 
European elm, fig. Old World grapevine, mulberry, peach, 
pecan, Persian walnut, weeping willow. 




Fig. 6. — Root-knot (nematode) on salsify. 
Original. 

In limited areas soil disinfection (p. 460) may be em- 
ployed. Thorough cultivation and fertilization induces the 
roots of perennials to extend deeper into the soil, thus reach- 
ing below the nematode zone, affording at least temporary 
alleviation. Three years of rotation with non-susceptible 
crops as corn, timothy, red- top, velvet beans, resistant 
cowpeas, barley, winter rye, or oats with care to keep down 
susceptible weeds largely reduces the amount of soil infection. 



26 Diseases of Economic Plants 

Certain varieties of cowpeas (p. 335), tobacco, grapes, figs, 
and watermelon show resistance. Calcium cyanamide, 
1,000 to 5,000 pounds per acre applied several weeks be- 
fore planting and followed by abundant water, reduces the 
number of nematodes. 

Hairy-root, also due to nematodes, is discussed on p. 162. 

Certain fungi as Penicillium (Soft-rot or Dry-rot) p. 51, 
Phytophthora omnivorum, Sclerotinia lihertiaiia (Drop, Wilt) 
p. 196, are so general in their habits as to be found on almost 
any host. 

Disease due to Impure Air.'-^* -^ — Plants are sensitive to 
certain chemical impurities of the air and may either be killed 
or greatly retarded in growth by them. These impurities are 
chiefly smoke and gases or solids resulting from industrial 
operations. The aerial emanations of smelters are of a 
character peculiar to the processes involved and of a quantity 
to make their effect apparent to considerable distances. It 
has been clearly shown that even small quantities of illumi- 
nating gas or sulfur dioxid are very deleterious in their 
effect upon plants. So marked are the effects upon vegeta- 
tion that definite zones of injury may be mapped in the 
vicinity of large air-pollution centers, the outer zone extending 
to a distance of from 75 to 100 miles. Illuminating gas es- 
caping from mains into the air of the soil frequently causes 
death of trees. There is considerable difference in resistance 
between different varieties of plants and if the air pollution 
cannot be abated the more resistant varieties should l)e 
planted. 

Soil diseases.-*^ — A group of plant diseases of special de- 
structiveness comprises those of which the causal organism 
resides in the soil from year to year ready to infect any 
susceptible crop planted thereon. 

Notorious among such are the wilts of the cotton, tobacco, 
tomato, cucumber, muskmelon, eggplant, cowpea, water- 
melon, cabbage, flax, sweet potato and potato; the club- 
root of cabbage and other crucifers; black-rot of similar 
plants; smut of onion. Other soil diseases are potato wart 



General Diseases 27 

and scabs, beet scab, lettuce drop, and numerous others 
mentioned on following pages as well as the general diseases 
discussed al)ove. Since these diseases are similar in their 
mode of multiplication and dissemination they are given 
general consideration here. 

The peculiar destructiveness of these diseases is due 
to the fact that they not only kill the crop, but they also 
prohibit successful culture of susceptible crops in succeeding 
years. This crop limitation, if the crop in question be an 
important one, perhaps the only really profitable one suited 
to the soil affected, may result in large depreciation in land 
values. 

It is unknown how long the germs can live in the soil 
without susceptible host plants. That they can live from 
one season to the second season following is certain. A 
field slightly affected one year, if put to a susceptible crop 
the second year after, will be even more seriously infested, 
and the trouble will grow so long as such crops are cultivated 
wdth but short intervening periods. Many cases are known 
where a rest of five and even eight years does not materially 
restore the soil to normal condition. 

The application of chemicals to the soil is of value only 
in rare instances, and even then is questionable. No means 
of soil disinfection applicable to fields is known. Land once 
infested, therefore, can become again usable only by eliminat- 
ing the causal organisms by a long system of rotation which 
is usually only partially effective, or by the use of resistant 
varieties of plants, and these in ziiost instances are not as yet 
known or do not as yet exist. 

In view of these facts it is especially necessary to stress 
the importance of protection of soils against infestation. 
To understand the means of protection the modes of dis- 
semination must be known. 

All plants affected with these diseases harbor immense 
numbers of the reproductive parts of the causal organisms, 
bacteria, spores, mycelium, sclerotia, etc. Upon the death 
and disintegration of the host plant they are liberated in 



I'M' 




General Diseases 29 

the soil, where they are able to live for considerable time, 
frequently for years. The immensity of their number in a 
diseased plant is inconceivable. Even a few diseased stems, 
roots, or leaves in the field will stock the soil thoroughly. In- 
fected plants, or soil in which infected plants have grown, or 
which bears parts of infected plants can therefore convey 
such contagion to new fields. 

Instances may be cited where the contagion has spread 
by washing from higher to lower land; moreover contagion 
may be carried by any means which can convey soil from 
one field to another, notably through tools which have 
been used on infested soil. Though apparently clean, such 
tools, if they bear even minute particles of soil, may convey 
hundreds of germs and thus start an epidemic in a field. 
The hoofs of animals or the feet of laborers may in a similar 
way bear disease-laden soil. Wind passing over an infested 
field may pick up broken bits of sick plants or germ-laden 
soil, and convey these to other fields. Infestation by wind, 
however, seems to be rare, possibly because of the ger- 
micidal action of the sun's rays upon the surface layer of 
soil upon which the wind must act. If the crop be one which 
is used for stock feed or one which may become mixed with 
stock feed, the organisms may be spread widely through 
manure which has here become infested from the feed 
(cf. watermelon, cabbage). 

A field may be protected from higher land that is in- 
fested by proper arrangement of dykes. In some cases a 
thorough cleansing of tools so that there is no possibility 
of conveying the germs will aid in repression. The dirt may 
be knocked off, then wiped off, and the implement finally 
disinfected with a solution of 2 per cent foraialin or 5 per 
cent carbohc acid. It is difficult to insure complete protec- 
tion against disease dissemination by the feet of animals and 
man, but if uninfested land remains to be protected, every 
precaution should be exercised in this particular. 

Where but a few plants in a field are affected, they should 
be removed from the soil and destroyed by fire, — root, 



30 Diseases of Economic Plants 

branch, and leaf. Prompt action here may materially 
lessen the rapidity of spread of the disease in the field. 
Every particle of the sick plant burned means the destruc- 
tion of millions of the causal organisms. 

A long rotation of crops, one that will bring the suscep- 
tible plant back upon the affected field only after an inter- 
vening period of several years, perhaps after a period of 
eight or ten years, is useful in some cases, notably with 
tobacco wilt and onion smut, though in other cases, notably 
watermelon wilt, such rotation is of httle avail. 

The one means of overcoming these soil diseases, which 
is most promising to farmers, lies in the discovery of a variety 
of the crop plant that will not succumb to attack even when 
planted upon infected soil. Varieties of cotton, tobacco, 
tomatoes, cabbage, flax, cowpeas, and watermelon that are 
resistant to their respective soil diseases have been dis- 
covered or developed by breeding. There is similar hope in 
regard to other crops. 



DISEASES OF SPECIAL CROPS 
POMACEOUS FRUITS 28 

The pomaceous fruit plants, owing to the fact that they 
are long-Hved perennials, that their products are standard and 
of high value, that they are universally grown throughout the 
United States, when subject to an injurious disease justify 




Fig. 8. — Apple bitter-rot in early stages showing acervuli. 
After Scott. 

careful consideration of the means of combating the disease 
and the employment of even expensive methods to attain 
the end. 



APPLE 

Bitter-rot '^^'^^ {Glomerella cingulata (Stonem.) S. & v. S., 
Gloeosporium) . The effect of the disease is seen upon both 
the fruit and the twig. Upon the fruit the rotten spot is 

31 



32 



Diseases of Economic Plants 



at first soft and wet, in later stages corky, more or less dry, 
and brown, tan-colored, or black. This spot under favorable 
conditions increases in diameter at a rate varying from 1- 
10 mm. each day. Single or numerous lesions may appear 
upon the fruit, depending upon the abundance of the infect- 
ing spores and their ability to gain access through the cuticle. 
When a spot becomes quite large, it is usually somewhat de- 
pressed, with a shriveled, 
wrinkled surface, due to 
loss of turgor of the un- 
derlying tissue caused by 
evaporation. As the spot 
ages minute spore-bear- 
ing pustules of the causal 
fungus, barely visible to 
the naked eye, appear, 
first at or near the center. 
The tissue of the fruit is 
affected to some depth, 
although the progress of 
the disease is not so rapid 
downward as laterally. 
The pulp of the apple at 
the margin of the rotten 
region is usually bitter, thus giving rise to the common 
name of the disease. 

Fruit of any age after its formation is liable to infection 
if suitable climatic conditions and infective material obtain, 
though the disease is most noticeable and does most damage 
as the fruit approaches maturity. A series of hot, wet days 
favors a destructive attack, while cold checks it. The fruit 
as soon as it is badly rotted usually falls from the tree, 
covering the ground beneath, while apples less advanced in 
disease still hang upon the limbs. 

This same disease occasionally affects twigs and young 
branches, causing cankers or rough spots in the bark. Young 
cankers are slightly rough, owing to the dead bark, and ex- 




FiG. 9. — Apple in advanced stage of 
bitter-rot. After Scott. 



Pomaceous Fruits 



33 



tend only partly around the twigs. Old cankers are very 
rough, and may extend several centimeters longitudinally 
along the twig, thus giving it a flattened appearance. 



^f 





•..^ ' '^*'v 



^ "^'--^ 






Fig. 10. — Bitter-rot cankers. After U. S. Dept. Agr. 



The fungus causing the rot upon the fruit was described 
in 1856 by Berkeley. That the cankers are caused by the 
same fungus was recognized independently by two research 
parties, Burrill and Blair, and von Schrenk and Spaulding 



34 Diseases of Economic Plants 

in 1902. Upon both twigs and fruit the spores are borne 
in great numbers. The fungus is, moreover, perennial 
upon the twigs, the cankers serving as initial points of in- 
fection for each year's epidemic. 

The natural course of the disease is through twig infec- 
tion; spores from some older lesion are transferred to points 
of weakness on the twig, such as bark ruptured from any 
cause. The fungus may also develop and overwinter in old 
cankers caused by other fungi, on dead twigs or scars on the 
fruit spurs, or even in the crevices in the bark and at these 
points produce spores the following year. These in turn, 
carried chiefly by rain, partly by insects, possibly birds, or 
other agencies, fall upon apples, and there initiate spots of 
rot. Apples thus infected serve as multiplying ground for 
the further infection of other apples. Six days after an apple 
is infected a crop of spores may mature and be ready to 
further spread the disease. To some extent the causal fungus 
hibernates in mummified fruits, which thus become sources 
of initial infection in the succeeding year. 

Bitter-rot occurs throughout the United States wherever 
apples grow, but has been most destructive heretofore in 
sections southwest of Virginia between the parallels of 35° 
and 39° north latitude. It is known also in comparatively 
harmless form in Europe and Australia. In 1900 it was esti- 
mated that the loss in four counties of Illinois was $1,500,000. 
The president of the National Apple Shippers Association 
estimated the damage to the apple crop of the United States 
that year as $10,000,000. There is often a loss of from 50 to 
75 per cent of the crop. 

Two modes of treatment are useful : fii'st, to cut off and 
burn the cankers in so far as is practicable, and to hand-pick 
and destroy mummified fruit; second, to spray the growing 
fruit with a fungicide. The trees should be sprayed fre- 
quently with Bordeaux mixture, or lime-sulfur (summer 
strength) from the time the petals fall until the fruit is almost 
ripe. A non-spotting spray should be used for the last 
application. Cf. p. 447. 



Pomaceous Fruits 



35 



Scab ^^' ^''' ^^^ {Venturia inoequalis (Cke.) Wint., Fusicla- 
diwn). — This is justly called the most injurious disease with 
which the apple grower has to contend. Originally imported 





-— r-r^^ 





Fig. 11. — Bitter-rot cankers in which perithecia were found. 

After Burrill. 

from abroad, the first record is in Europe, 1819. Later it 
was noted in America, both in New York and Pennsylvania, 
in 1834, whence it apparently spread westward. It affects 



36 



Diseases of Economic Plants 



both fruit and leaves, probably in all localities where apples 
are grown, and is serious in Europe, Australia, Africa, and 
New Zealand, as well as in America. 

Upon the fruit, the scab first causes the skin to take on 
a dark olive-green color; later, as the outer skin breaks and 




Fig. 12. — Apple scab. After Craig. 

exposes the fungus underneath, the color changes to black. 
An apple in this stage is shown in Fig. 12. Still later the 
scab enlarges, and the spores and fungous cells at the center 
of the spot may fall away, leaving a skin of rusty appearance 
surrounded by a dark ring where the fungus has not yet 
fallen off. Farther from the center of the spot may be an 
olive-green or silvery ring, showing the still younger stage of 
the disease. Cracking and distortion occur in cases of very 



Pomaceous Fruits 



37 



badly affected fruits. Scabby fruits are much more sus- 
ceptible to storage rots than are clean fruits (p. 49). 

Upon the leaves and more rarely upon twigs the fungus 
forms a thick velvety coat, varying from dark olive-green to 
black, in spots at first circular in outline, later irregular and 
coalescing. The irritation and retardation of growth caused 
by the presence of the fungus often induces the leaves to curl 
and wrinkle in a characteristic manner. The fungus winters 
on fallen leaves, and wind-borne spores from them give rise to 
spring infection. Cf. pp. 58, 60. 

The injuries by this disease may be enumerated as fol- 
lows: lessened leaf value, retarded twig and wood growth, 
premature fall of fruit, 
retardation of full de- 
velopment of fruit, and 
injury to sale and keep- 
ing quality of fruit. 

Baldwin, Golden Rus- 
set, and Hubbardston 
are among the most re- 
sistant varieties, though 
scab-resistance seems to 
vary geographically and 
even seasonally. Cf. 
p. 60. 

Bordeaux mixture and 
lime-sulfur are effective 
sprays. It is especially 
important to apply the 
mixture immediately be- 
fore the blossoms open, again just after the petals fall, fol- 
lowed by one or two later sprayings. Cf. p. 57. Dusting is 
discussed on page 446. Burning of infected, fallen leaves is 
a good sanitary measure. 

Blotch ^^"^o- ^-1 {Phyllostida solitaria E. & E.). — In some 
sections of the country this disease of bark, leaf, and fruit is 
even more troublesome than any of the preceding, though its 




Fig. 



13. — Apple blotch, 
and Rorer. 



After Scott 



38 



Diseases of Economic Plants 



distinct identity was not recognized until 1895. Since then 
the disease has been observed in the Eastern and South- 
eastern states, though not in 
serious form. Its most destructive 
center, heretofore, has been in the 
Ozarks of Arkansas and Missouri 
and in southern IlUnois, Ohio, and 
Indiana where a large per cent of 
the crop is commonly rendered 
unfit for barreling. One county 
alone in Arkansas is estimated to 
have suffered a loss of $950,000 in 
1906. Owing to its superficial 
similarity, blotch has been con- 
founded with scab in some in- 
stances. The first publication con- 
cerning the disease appeared in 
1902, and the first detailed de- 
scription in 1907. 

Upon fruit the blotches are from 
5-20 mm. in diameter, dark in 
color, with an advancing margin 
of peculiar, irregular, jagged, or 
fringed appearance. By coales- 
cence large spots may form, and 
owing to tension, cracks appear, 
enlarging to a centimeter in length, 
or even girdling the fruit, and 
reaching to the core. In the older 
portions of the blotch, minute 
pycnidia develop. These blotches 
mar the appearance of the fruit 
and injure it as a salable product. 

Upon twigs, spurs, or shoots are produced cankers, which, 
during the first year, consist of small spots 2-10 mm. in 
diameter, tan-colored, each bearing several pycnidia. The 
margins of the spots are sharply limited, and are usually 




Fig. 



14. — Apple blotch on 
twigs. Original. 



Pomaceous Fruits 



39 



bordered with a narrow red line. In older cankers the 
diseased bark becomes cracked, furrowed, and much rough- 
ened. 

On the leaf this fungus causes small, regular, light brown, 
yellowish, or whitish spots, 
usually 1-2 mm. in diameter, 
each of which may bear one 
or several pycnidia. 

The Ben Davis, Missouri 
Pippin, Limber Twig, and 
Maiden Blush are highly sus- 
ceptible, while Winesap, Jona- 
than, and York Imperial are 
almost immune. 

Ordinarily three applica- 
tions of 3-4-50 Bordeaux 
mixture suffice to control 
blotch. The first spraying 
should be made two or three 
weeks after the petals have 
fallen; the second about two 
weeks later; the third two 
weeks thereafter. Lime-sulfur 
should be substituted during 
wet weather to avoid Bor- 
deaux injury. Careful prun- 
ing to remove affected twigs 
is beneficial. 

Rusts ^^' ^^' ^^^ (Gymnospor- 
angium sps., Roestelia). — 
Rusts of the apple may usually 
be recognized by their char- 
acteristic spots on the leaf, or more rarely upon the fruit or 
twig. These spots, yellowish green at first, gradually become 
darker, approaching orange. Upon close examination, the 
upper surface of one of these discolored spots is seen to con- 
tain numerous pustules, at first honey yellow, finally black, 




Fig. 15. — Apple leaf affected 
with rust. After Anderson. 



40 Diseases of Economic Plants 

smaller than a pinhole, while upon the lower surface of the 
diseased spot appear some weeks later the fringe-toothed 
cluster-cups. This spot is sometimes so abundant that its 
presence upon orchards may be recognized at great distances 
by the characteristic hue imparted to the foliage mass as a 
whole. Rust robs the tree of nourishment and renders normal 
fruitage impossible. 

A peculiar relation exists, in that the causal fungus spends 
part of its life on one plant, the apple, and the remainder 
upon a totally different plant, the red cedar (Juniperus), the 
Alternate Host of the apple rust. The fungus summers upon 
the cultivated apple or the wild crab-apple tree, from which 
later spores are borne by the wind to adjacent juniper or 
red cedar trees. There the fungus grows and causes the 
familiar ''cedar apple." 

In the spring the. cedar apple produces gelatinous, horn- 
like projections, each bearing myriads of spores, which, 
when conveyed by the wind to the susceptible apple tree, 
under suitable conditions, cause the apple rust. Evidence 
that this relation really exists is readily found if one ex- 
amines an orchard having red cedar trees upon its windward 
boundary. 

It is clear that the more red cedar trees there are in the 
neighborhood of an orchard, especially to windward, the 
more probability there is of damage from the rust. The 
rational treatment, therefore, is to remove these trees in 
so far as possible, or if the value of the cedar warrants it to 
hand-pick the cedar galls. 

In rare instances spores may be carried several miles, but 
orchards are reasonably secure if all possibility of infection 
from the immediate neighborhood be removed; that is to 
say, for a radius of two miles. In case the red cedars are too 
numerous, or if for other reasons it is impossible to cut them, 
spraying the apple trees at a time corresponding with the 
spore discharge from the cedar-galls will lessen the evil, but 
the success of spraying is neither complete nor certain. 

Resistant apple varieties are : Yellow Transparent, Maiden 



Pomaceous Fruits 



41 



Blush, Baldwin, Grimes, Stayman, Winesap. The following 
are more susceptible: Wealthy, Jonathan, Rome, York 
Imperial, Ben Davis, Greening. 

Fire-blight^^ (Bacillus amylovorus (Burr.) Trev.). — De- 
scription and discussion of this disease will be found on 




Fig. 16. — A cedar apple in condition to give off spores. 
After Anderson. 

page 62 under pear, the blight of which is identical with the 
apple disease. Its character and treatment are the same upon 
both hosts. While the bhght is preeminently a pear disease, 
it also affects the apple very seriously, particularly in the 
form of blossom-blight and body-blight. 



42 



Diseases of Economic Plants 



The Lowell, Isham, Smith Cider, Yellow Transparent, 
Jonathan, and Willow Twig are especially susceptible 
varieties, while Celestia, Buckingham, Mammoth Black 
Twig, White Winter Pearmain, Winesap, and Ben Davis 

are resistant, the last almost en- 
tirely so. In general the crab vari- 
eties are more susceptible than 
others. 

Black-rot, canker ^4. 45 (Physalo- 
spora cydo7ii(B Arn., Sphceropsis) . — 
In many respects this disease closely 
resembles the bitter-rot, particu- 
larly in that it appears both as rot 
of the fruit and as cankers upon 
the limbs. In some instances it 
also appears as a twig blight and 
as a leaf spot. As seen under the 
hand lens the coils of exuding 
spores are black, instead of pink, 
as is the case with bitter-rot. A 
compound microscop-'^ is necessary 
to bring out other distinguishing 
characters. 

The limb cankers, first studied 
by Paddock, consist of swellings, 
with the bark rough, and black. 
In other cases the black, decayed 
wood from which the bark has dis- 
appeared is exposed. This cankerous infection sometimes ex- 
tends for nearly a meter along the branch, and occasionally 
girdles it. When occurring upon the trunk or main branches 
it is called black-rot body-blight. 

The Tolman Sweet is said to be quite resistant to canker, 
while Twenty Ounce is very susceptible. Four other va- 
rieties range in susceptibility as follows: Baldwin, Wagener, 
Greening, King. 

Black-rot twig-blight somewhat resembles fire-blight with 




Fig. 17. — Apple black-rot 
canker showing numer- 
ous pycnidia. After 
Whetzel. 



Pomaceous Fruits 



43 



which it is often associated, but may be distinguished 
from it by the presence of myriads of minute pimples 
distributed thickly over the affected region. With a hand 
lens coils of spores may often be clearly seen issuing 
from these pustules. 

Upon the leaf, 
blighted spots are 
produced, irregularly 
circular in outline, 
often marked by 
concentric rings. 
The body of the 
spot is brownish and 
the margin sharply 
limited. Similar 
spots are caused in 
several other dis- 
eases, and definite 
knowledge of the 
nature of leaf spots 
must depend upon 
microscopic diagno- 
sis in each special 
case. 

The various forms 
of this disease which 
have been noted 
above are found in 
Nebraska, Michi- 
gan, the Ozarks, 
Ohio, Wisconsin, and 

throughout the Allegheny and eastern apple sections, and 
are troublesome each year. 

The treatment should be the same as that recommended 
for bitter-rot with special care to avoid bark wounds of 
all kinds, as from ladders and workmen's boots. 

A rot upon fruit very similar to bitter-rot, and a twig- 




FiG. 18. — Pacific coast canker. After 
Cordley. 



44 Diseases of Economic Plants 

blight very similar to that of black-rot, though less important, 
is caused by Coniothyrium fuckelii Sacc.^*' 

Pacific coast canker ^^' ^^ (Neofabroea malicorticis (Cord.) 
Jack., Gloeosporium) . — The Pacific coast canker, first noted 
about 1893, is particularly destructive in the Northwestern 
states and British Columbia west of the Cascade Mountains. 

The bark or sapwood of twigs and larger branches is the 
seat of infection, but the disease may occur also upon the 
fruit when in storage. The loss of an entire orchard within a 
few years has resulted. Young trees, owing to their tender 
bark, are especially susceptible. 

Upon twigs, cankers in the early stage appear as round or 
oval, slightly sunken, dark areas which increase but slowly 
in diameter. As soon, however, as the fungus penetrates 
into the cambium and sapwood the canker enlarges very 
rapidly, making its most rapid development through the 
cambium, and advancing more tardily through the overlying 
bark. The resulting spots are nearly circular, quite black, 
and from 5 mm. to 12-14 cm. in diameter. When old, the 
bark becomes brittle and a definite fissure separates the dead 
from the healthy portions, indicating cessation of advance of 
the fungus. The diseased bark eventually falls away, leaving 
a scar. Branches, or even trees, may be killed by girdling 
cankers. 

Upon stored fruit the disease appears first as light-brown, 
circular, rotten spots. These later turn very dark or black, 
and become depressed, dry, and tough. Acervuli similar 
to those upon the bark soon develop in concentric circles. 

When the cankers are few, on small trees, excision may 
be practiced to advantage; when, however, there are hun- 
dreds of cankers upon each tree, this treatment is manifestly 
impracticable. Spraying with strong Bordeaux mixture in the 
fall, after the crop is gathered and again after an interval of 
about three weeks, is valuable to prevent the formation of new 
cankers, and has established practical control of the disease. 

Blister-canker "^^"^^ {Nummularia discreta (Schw.) Tub). — • 
Attention in America was first called to this active, parasitic 



Pomaceous Fruits 



45 




disease in 1902 by Hasselbring, who attributed to it more 
serious results than from any other canker disease of IlHnois. 
In many cases large limbs and even whole trees are killed. It 
has been reported in many states, including Arkansas, Okla- 
homa, Nebraska, New Hampshire, New York, and Virginia. 

The cankers are at first in- 
conspicuous, unhealthy, dirty 
brown, usually depressed 
spots in the bark, sometimes 
15 cm. in diameter, which 
enlarge rapidly, particularly 
lengthwise upon the limb, a 
crack often marking the 
boundary between dead and 
sound bark. The interior of 
the bark of such spots is 
mottled with dead regions. 

In autumn the sporiferous 
bodies appear near the bor- 
ders of the diseased spots, first 
pushing through cracks in 
the bark, and exposing pale 
grayish ochre-colored fungous 
growths 3-6 mm. in diam- 
eter,which, when mature, are 
slightly saucer-shaped, and 
dark in color. These bodies 
are attached to the dead 
wood, and remain there even 
after the bark has fallen 
away, thus constituting a 

diagnostic character of absolute reliability, separating this 
from all other cankers. Discoloration of the heartwood 
often occurs at a distance of a meter or more from the ap- 
parent seat of disease. 

When the cankers become large, injury to the distal parts 
through interruption of the water supply results. The 




Fig. 19. — Black-spot on fruit. 
After Lawrence. 



46 



Diseases of Economic Plants 



leaves show symptoms of disease, and the fruit fails to grow 
to full size. With complete girdling the limb dies. 

Since all infection seems to occur through wounds, pre- 
vention must look largely toward the avoidance of wounds 




Fig. 20. — Blister-canker. Some of the discs have been re- 
moved to show the underlying marking. 

by tools, machinery, harnesses, pickers' ladders, boots, etc. 
It is also an excellent sanitary measure to cut out and burn 
all infective material, and in incipient cases excision of 
diseased tissue in a limb may be practiced with profit. 



Pomaceous Fruits 



47 



Leaf-spots ^^"^^ (various fungi) (see also black-rot, p. 42). 
— Aside from the leaf diseases of apple already mentioned, 
there are numerous other leaf-spots due to various causes. 
These spots partake of the same general character. That is, 
they are brown to tan-col- 
ored, at first circular, later 
irregularly circular, defi- 
nitely bordered, and usually 
concentrically marked. If 
abundant, or if they enlarge 
rapidly upon the leaves, 
they cause their premature 
fall, and largely defoliate ; 
the tree. Such spots pre- 
vail to greater or less ex- 
tent in all apple orchards 
but are most destructive 
in the Southern states. 
Numerous species of fungi 
have been isolated from 
these spots; some of them 
undoubtedly sustain a 
causal relation to the dis- 
ease. Sheldon claims that 
in West Virginia much of 
the apple leaf-spot is due 
to an Illosporium. 

Whatever the actual 
ijausal fungi may be, these 
spots are all, or nearly all, 
of fungous origin and are 
amenable to preventive 
spraying. The first of three or four applications should be 
given with the opening of the leaf buds. 

Rypochnose ^^^ ^'^ {Corticium stevensii (Noack) Burt). — 
Superficially this disease resembles the bhght, with which it 
is likely to be confounded by the casual observer. It may 




Fig. 21. — Apple leaf-spot in late 
stage of development, showing 
concentric rings. Original. 



48 



Diseases of Economic Plants 



readily be distinguished, however, by two characters: first, 
the manner in which the leaves droop and mat together, 

which is quite different 
from the habit of the 
blight, the leaves of 
which neither droop nor 
become matted; second, 
by the presence of small 
sclerotia, white when 
young, cinnamon-brown 
when mature, upon the 
twigs adjacent to the 
affected leaves. These 
sclerotia usually meas- 
ure about 2-3 mm. 
in diameter. Together 
with the sclerotia and 
extending along the 
twig longitudinally are 
also found silvery, glis- 
tening, thread-like, fun- 
gous growths. 

This fungus hiber- 
nates in the sclerotia 
on or near the terminal 
bud and thence invades 
the new twigs as they 
develop, reaching out 
upon each leaf, spread- 
ing over its under sur- 
face in almost invisible 
thinness, and causing it 
to droop, die, and eventually to fall away. Thus, in early 
autumn, such trees are nearly or quite defoliated. The 
fruit may also be invaded by the fungus. 

Hypochnose, first described from Brazil, is known from 
Maine to Florida and Texas. It seems to be especially de- 




i^ IG. 22. — Hypochnose, showing mat- 
ting of leaves. Original. 



Pomaceous Fruits 



49 



structive in regions of exces- 
sive humidity, particularly 
in the deep mountain valleys 
of the Appalachians, where 
whole orchards are some- 
times seriously affected. 

Owing to the entirely su- 
perficial nature of the fungus 
which causes the disease, 
and its habit of hibernating 
upon the twigs, the trees 
should be sprayed with a 
strong cleansing mixture, 
Bordeaux or bluestone, be- 
fore the buds open, and 
again just before the blos- 
soms open. 

Pink-rot ^^ (Cephalothe- 
cium roseum Cda.). — This 
rot is known in many states. 
It follows apple or quince 
scab and may be recognized 
by the white, mildew-like 
growth which appears in 
conjunction with the scab 
which it soon after entirely 
overgrows and turns to a 
pink color. 

While the decay is really 
caused by Cephalothecium, 
a rupture made in the skin 
by the scab fungus is the 
usual place of entrance. The 
decayed spot is shallow and 
slow-growing as compared 
with other rots. It is ac- 
companied by a bitter taste 




Fig. 23. — Hypochnose, showing 
sclerotia on twig at left and rhi- 
zomorphic strands on twig at 
right. Original. 



50 



Diseases of Economic Plants 



which is so pronounced as to injure cider made from affected 
apples. The chief destruction follows the harvest, though 
the disease is sometimes found in fruit still upon the tree. 

The Rhode Island Greening, Fall Pippin, Fameuse, 
Maiden Blush, Tompkins King, and Twenty Ounce are 
especially susceptible. 

Chief attention should be directed to the prevention of 




Fig. 24. — Pink-rot following scab. 
Anderson. 



After 



scab. In storage a dry house, well ventilated, kept at 0° C. 
(32° F.) gives best rot resistance. 

Another form of pink-rot due to a species of Hypochnus 
has been described by Eustace ^^ especially upon Baldwins 
and Rhode Island Greenings. There is no large surface 
growth of the fungus on the diseased spot, but the rot often 
extends to the core. 

Powdery-mildew ^^' ^^ {Podosphceral eucotricha (E. & E.) 
Salm., Oidium). — The general appearance of this mildew 
is similar to grape mildew; that is, the surfaces of the leaves 



Pomaceous Fruits 51 

are more or less covered with a white or grayish fungous 
growth, in the later stages of which are found numerous very- 
small black fruiting bodies approximately 0.25 mm. in 
diameter. This fungus, while of comparatively little sig- 
nificance to old apple trees, causes much injury to nursery 
stock, often becoming so serious as to prevent successful 
budding. Mildew has been reported as especially serious in 
California and other states west of the Rocky Mountains, 
and is of some importance in all apple regions. In the Pajaro 
Valley the fungous mycelium has been shown to hibernate 
in the buds, resulting in early spring infection of shoots. 

Another species of mildew, P. oxyacanthce (DC.) De Bary, 
shows the same general characters as the mildew described 
above, but is of less economic importance. Three or four 
lime-sulfur sprayings at intervals of about two weeks, 
beginning when the buds commence to open, have given best 
results. 

Crown-gall. See peach. 

Soft-rot, blue-mold, rot {Penicillium expansum Lk.) . — Per- 
haps the most common apple rot is found upon stored apples 
late in the year. The light, tan-colored rotted area is soft 
and watery. The decay results in the complete loss of the 
affected fruit, and, by contagion, in loss to the fruit mass. 

Upon cracks in the decayed surface, and eventually over 
the whole rotten part, appear tufts of very short delicate 
fungous threads, at first white, soon bluish-green, very like 
the common blue-mold so familiar to the housewife upon 
canned fruit, the seal of which has permitted air to enter. 
This blue substance upon the rotten apple consists of myriads 
of the spores of the causal fungus. This fungus is compara- 
tively unaggressive and cannot force its way into perfectly 
healthy tissue; a bruise or rupture of the skin is necessary 
to its invasion. The best preventive is care to avoid bruising. 

Root-rot ^^ (various fungi). — Death of trees, without 
apparent reason from evidence above ground, is frequently 
due to disease and decay of the roots. While the earlier 
symptoms may vary, in general they include an abnormally 



52 



Diseases of Economic Plants 



large set of small fruits, and in the following season few 
flowers, deficient growth, and small leaf development and 
perhaps chlorosis. In cases where only a few roots are 
diseased the evident effects may be limited to the correspond- 




FiG. 25. — Clitocybe upon apple. After Wilcox. 

ing side of the tree. Several years may elapse between the ap- 
pearance of the first symptoms and final death. The roots, 
one or all, of trees well advanced in disease show decay, de- 
pendent in character upon the causal fungus. Several dif- 
ferent fungi cause root-rot (see p. 370). Among those most 
common on fruit trees are: Clitocybe parasitica Wil. A 



Pomaceous Fruits 



53 



gummy exudate is usually present around the base of the tree 
and black rhizomorphs adhere to the roots. In late stages 
clusters of the gill-bearing sporophores (Fig. 25) develop; 
Ar77iillaria mellea Vahl. Quantities of black, stringy, hard, 
shiny strands 1 to 2 mm. in diameter occur around the roots 
and in the adjacent soil. The gilled sporophores appear later 
(p. 370); Fomes annosus (Fr.) Cke. The sporophores are 
pore-bearing (p. 371); 
Septohasidium sps. with 
smooth pore-bearing 
surfaces; Ozo7iium om- 
nivormn Sh. See Texas 
root-rot (p. 23); Xyl- 
aria sps.^^ The affected 
roots are covered with 
a thin, compact growth 
of mycelium, white at 
first, later developing 
into a black incrusta- 
tion. Minute, thread- 
like rhizomorphs ra- 
diate several centime- 
ters along the root. 
Affected roots are soon girdled and the distal parts die. 

Root-rot, due to one or another of these causes, is of wide 
and common occurrence, and results in large loss. It is 
found more frequently on newly cleared land than elsewhere. 
When the disease has advanced far enough to be recognized, 
no cure is available, and it is unsafe to replant in the infested 
place. Wood bearing root-rot fungi should be burned to 
lessen infection. 

Wood-rot ^'' of orchard trees is of the general character dis- 
cussed under Decay in live trees on page 354. It is a very 
important source of loss on fruit trees of all kinds, about 
one-half of all bearing trees being infected. The rot may 
chiefly be avoided by preventing wounds or by treating them 
with disinfectants. See p. 378. 




Fig. 26. - 
lation. 
ters A. 



- Brown-rot produced by inocu- 
Note the fungus forms the let- 
M. G. Original. 



54 Diseases of Economic Plants 

Frost Injury. ^^ — Varieties of apples differ from each other 
in their susceptibihty to injury from cold. The injury may 
be local, on single twigs, or spots on twigs, body, or branch; 
or general, affecting the whole tree. The damage may be 
apparent externally or show at first only in a discolored 
cambium. '^ Sun scald," in which the frosted bark occurs as a 
cankered area and either peels off, or clings tightly and is 
sunken, is a frost injury. Twigs may be killed outright, 
especially if the wood has not ripened properly. Late spring 
frosts injure, as is well known, the buds, blossoms, etc. 
Frost cankers may form the threshold for the entrance of 
various fungi and thus pave the way to disease, e. g. black- 
rot or bitter-rot cankers. A cover crop tends to lessen frost 
injury, by diminishing excess moisture in the fall, while 
avoidance of cultivation late in the season hastens maturing 
of the wood. 

Bitter-Pit ^^ consists of a pitting of the fruits with slightly 
sunken circular spots varying from mere dots to 5 mm. in 
diameter, which finally become brown. The tissue at the 
bottom of the pit is dead, brown, and spongy. Similar lesions 
may occur deep within the tissue of the apple. No parasite 
is present and the trouble seems to be due to improper water 
relations. The disease causes considerable loss over a large 
range of territory. Thinning the fruit to a proper set lessens 
the damage. Pitted fruit should either be consumed at 
once or stored or shipped under low-temperature conditions 
(30°-32° F.,— 1°-0° C.) 

Jonathan-Spot^^' ^^^ occurs on several varieties of apples 
including the Jonathan, Esopus, Wealthy, Ortley, and Wolf 
River. The spots are circular, 2-15 mm. in diameter, 
abruptly but sKghtly depressed, light brown in color, and 
are more superficial than those of bitter-pit. The disease 
may appear on fruit still on the tree or may develop during 
storage or transit. The cause is unknown. Fruits of variety 
tending to spot should be consumed early or placed in cold 
storage. 

Scald ^^^ is a storage trouble particularly serious on im- 



Pomaceous Fruits 55 

mature apples. It is due to gases given off from apples and 
may be avoided by aeration. 

Minor diseases. 

European canker -^^ {Nectria galligena Bres.). — The Euro- 
pean canker was not recorded upon the apple in America 
prior to 1899, when Paddock mentioned its presence in Nova 
Scotia and New York. Later it was noted in New Hampshire 
and Ohio and is now known to be widely distributed from 
the Atlantic to the Pacific. It constitutes a serious disease 
in Europe and may become of importance here. The canker 
enlarges year after year, but more slowly than black-rot 
canker, and displays, when fruiting, numerous minute, deep 
red perithecia which serve to distinguish it from other 
cankers. 

Brown-rot ^° {Sclerotinia cinerea, Monilia) . — One of the 
most serious apple rots in Europe, this disease fortunately is 
not as yet destructive in America, though Sclerotinia cinerea 
is occasionally met with as one of the minor causes of apple 
losses. It has been observed in several states, notably New 
York, Missouri, Nebraska, the Virginias, North Carolina, 
Illinois, Minnesota, Arkansas, and New Mexico frequently 
enough to call for printed mention. Brown-rot produces 
complete decay of the affected apples, which turn brown, or 
later black, become soft and wrinkled, and soon show pustules 
of bushy mycelium breaking through rifts and fissures in the 
skin over the diseased tissue. The diseased fruits may 
mummify upon the tree or more frequently fall to the ground 
and there shrivel to dry, hard, wrinkled masses, in which the 
rot fungus winters. 

Sooty-blotch^^- (Glceodes pomigena (Schw.) Colby). — 
Irregular, sooty, black blotches, especially conspicuous on 
the lighter colored varieties of apples, are frequently seen 
upon unsprayed fruit. The individual blotches measure 
from 0.5-2 cm. across and are often so abundant that they 
coalesce, giving the fruit a dirty appearance. The fungus 
attacks the fruit late in the season, and is strictly superficial. 



56 



Diseases of Economic Plants 



It may easily be rubbed off with a cloth. The loss in ready 
salability, due to the unsightliness of the fruit, is reason 
enough for protective sprayings. Bordeaux mixture applied 
at intervals of about two weeks from the middle of June until 
the middle of August is effective. 

Fly-speck. ^^" — Growing upon the surface of the fruit and 
forming numerous clustered black specks closely resembling 




Fig. 27. — Fly- speck (at left); Sooty-blotch (at right). After Colby. 

fly-specks, this fungus causes disfigurement of the apple. 
The generic position of the fungus is in doubt, though it 
was originally named Lahrella pomi by Montague. 

Volutella rot^^ (Volutella frudi S. & H.). — In general 
appearance the volutella rot is not readily distinguished from 
black-rot, though the texture of the rotted tissue is much 
firmer and drier. Under the hand lens the sporiferous 
pustules are seen to be clothed with numerous hairs, which 
character sufficiently marks it as a separate disease. It has 
been reported from North Carolina, New York, Wisconsin, 
and is probably of general distribution. 

Scurf, an affection of the bark of twigs, is due to Phyllo- 
sticta prunicola (Opiz.) Sacc; Bark-canker '^ due to Myxospo- 



Pomaceous Fruits 57 

rium corticolum Edg. is superficial on both apples and pears 
and of little importance; the Fruit-spot, ^^' "^^ (Phoma pomi 
Pass.), occurs in the northeastern United States, the spots 
are small, sunken, brown or black; Rough-bark^- is caused 
by Phomopsis mali Rob. The Septobasidium canker is 
due to Septobasidium pedicillatu7n (Schw.) Pat. Phytophthora 
cadorum (L. & C.) Schr. causes a fruit rot. Black-mold, 
due to Fumago vagans, is superficial, while black-mold due 
to Alternaria sps. produces a core rot. Plenodomus can- 
ker ^^° (Plenodomus fusco-maculans (Sacc.) Coons) kills the 
cortex, which eventually flakes off in long strips leaving 
the wood bare. Die-back canker ^^^ (see peach) is occa- 
sionally present, also Fruit rots due to Endomyces and 
Rhizopus. Rosette, which resembles peach rosette, has 
been noted in three states. 



Conditions Infi<uencing the Spraying Schedule for 

Apple Disease * 

A spraying schedule which may give the best result in one 
part of the country when used in spraying a certain variety 
may be unsatisfactory in another part of the country, or 
for another variety or in another season, or in another 
orchard in the same part of the country. No attempt is 
made, therefore, to present definite spraying schedules, al- 
though an attempt is made to present briefly the considera- 
tions which govern them. 

Primarily, sprays are applied commercially to control 
apple scab, apple blotch, and bitter-rot. The control of other 
fungi with the exception of apple rust is usually incidental to 
the control of these three. 

To secure the best results it is necessary to make the first 
application of fungicide before the first infections take place, 
and to repeat at sufficient intervals to give protection from 
this time on. In general, it may be said that the first apple- 

* Prepared by W. A. Ruth. 



58 



Diseases of Economic Plants 



sc9.b infections usually occur about the time the trees are 
blossoming, and that serious damage may be caused by in- 
fections taking place for four or five weeks after the petals 
have fallen; that the first serious infections of apple blotch 
may take place three or four weeks after the petals have 
fallen, and that further infections, resulting in serious damage, 
may occur for a period of five or six weeks; that the first 
infections of bitter-rot may occur about the middle of June, 




Fig, 28. — Unsprayed apple trees. After Scott and Rorer. 

the period of possible infection continuing throughout the 
season, the probability of infection being greatest in hot, wet 
weather. 

The choice of the fungicide and the decision as to when to 
spray are governed by several considerations. These include 
the local conditions, among which may be placed varietal 
susceptibihty to apple scab, and the probable local varietal 
susceptibility to other fungi, seasonal weather conditions, 
and varietal susceptibility to spray injury. 

Locality. — Apple scab, apple blotch, and bitter-rot are so 



Pomaceous Fruits 



59 



distributed, as to the localities in which they produce serious 
injury, that in the northern apple-growing regions of the 
eastern United States orchardists spray chiefly to control 
apple scab; in southern apple-growing regions, it may be 
necessary to control apple scab, apple blotch, and bitter-rot; 
and in other regions to control scab and blotch. The general 
climatic relationship of these fungi in the eastern United 
States may be illustrated roughly by their behavior 



m 











■^')^ 


^ «A '^ 


'■f-r" 


f 
1^^' 




^^kL 




M . 










wBm' 




1 




■ 






^^^3 









Fig. 29. — Sprayed apple trees from the same orchard as those 

shown in Fig. 28. 

Illinois. Apple scab is a serious disease in all parts of the 
state; apple blotch is a serious disease as far as 40° north 
latitude; and, ordinarily, bitter-rot does not cause serious 
damage north of 39° latitude. It is thus necessary, in the 
northern part of the state, to spray for apple scab only; 
toward the southern part, it is necessary to spray for apple 
scab and apple blotch; and still farther south, to spray to 
control apple scab, apple blotch, and bitter-rot. 



60 Diseases of Economic Plants 

The relation between the apple and its parasitic fungi 
seems to vary, however, within more restricted areas. This 
may be illustrated as follows: The practice in the eastern 
United States has been to apply the first spray for apple 
scab just before the blossoms open, when the flowers in the 
cluster have separated from each other, and the pink petals 
are showing. (This is called the "pink," or '^ cluster-bud," 
spray.) Wallace, ^^ after studying the period of ascospore dis- 
charge, stated, in 1913, that there seems to be little danger in 
New York that infections of apple scab will occur much 
earlier than blossoming time, and that the cluster-bud spray 
is sufficiently early. Childs,^^^ as a result of similar study, 
later showed that, in Oregon, two applications must be made 
before the bloom, the first coming when the leaves are quite 
small, followed by the "cluster-bud" spray. Since then 
various spraying schedules have been worked out experi- 
mentally in the East. Thus, Blair ^^° in Nova Scotia, recom- 
mends two applications before the bloom, while Morse's 
work ^^Mn Maine may be taken to show that in the locality 
from which his data were drawn little or no infection occurs 
before the blossoming period. 

The relation differs not only with the locality but also with 
the variety of apple. Varietal susceptibility to or immunity 
from attack by one fungus is not necessarily correlated with 
the same relation toward another. This relationship seems 
to require local determination. The most susceptible va- 
rieties demand, of course, the most thorough treatment. 
The subject of varietal susceptibility to apple scab has been 
summarized by Wallace. ^^ (1) Certain varieties may appear 
to be immune in one season but may be very susceptible in 
another season, under different weather conditions. (2) A 
variety may be resistant in one year and susceptible in an- 
other year under conditions which for average varieties are as 
favorable to the disease in the one case as in the other. 

(3) Varietal susceptibility may differ in different localities. 

(4) Only in rare cases is a variety consistently and relatively 
immune over as short a period as five years. The apparent 



Pomaceous Fruits 61 

immunity may increase or decrease. (5) No variety is abso- 
lutely immune. 

Varietal susceptibility to scab differs so markedly in 
different localities that general lists are of little value. The 
Ben Davis, for example, which is generally considered rela- 
tively immune to scab, is very susceptible in Illinois. The 
Yellow Transparent, stated to be seriously injured by scab 
in Ohio, ^^" is relatively immune in southern Illinois, and the 
Grimes, which, in Ohio, is moderately injured by scab, is 
relatively immune in Illinois. The Rome Beauty is seriousty 
injured in both localities. 

Weather Conditions. — Weather conditions play a very 
important role in the outbreak of a disease. Wallace ^^ 
states that "The ideal condition for scab infection is a gentle, 
continued rain followed by cloudy, calm weather and a 
saturated atmosphere, in which cases the spores are kept 
wet for a long time in one position. Ascospores have been 
known to germinate in a period of four hours, but it is 
probable that in order to produce abundant infection 
the trees must be kept wet for eight or ten hours or 
even longer." Ascospore discharge begins almost as soon 
as rain begins, or within five minutes after the time the 
leaves are wet and, under continuously wet conditions, 
an interrupted discharge of spores can be expected for 
some time.^"* 

Roberts ^^ states that the dependence of apple-blotch 
infection upon rainy weather in orchards in the Ozark section 
is very noticeable, but in Kansas, where the sources of infec- 
tion — that is, the twig cankers — are much more numerous, 
the dependence is less noticeable. 

"The conditions most favorable for the development of 
bitter rot are (1) a period of hot weather accompanied by 
frequent rains and heavy dews at a period when the apple 
crop is approaching maturity, i. e., from the middle of July 
to the end of August. (2) Numerous sources of infection, 
i. e. cankers on the limbs and mummified fruits left hanging 
on the trees." Blair,^^ from whom the above is quoted, sum- 



62 Diseases of Economic Plants 

marizes the results of observation covering six years in 
Illinois as follows: 

''It may be safely concluded that moist weather with a 
considerable precipitation and a high temperature are 
favorable to the spread and growth of bitter-rot. There was 
no opportunity to note the effect of moist, cold weather 
though it might be argued from analogy, there being no 
evidence of the disease in northern and very little in central 
Illinois, where the rainfall is abundant and the mean tempera- 
ture lower, that moisture without high temperature is not 
favorable to the development of the disease. Hot weather 
alone unaccompanied by moisture proved unfavorable to 
the spread of the disease, as seen in the season of 1901, 
but hot weather alone did not prevent the disease from 
accomplishing its work of destruction after infection had 
once occurred, as was observed in 1900 when the dry month 
of August followed the abnormally wet months of June 
and July." 

The spraying schedule should be adjusted to meet the 
weather conditions. Rainy weather not only provides 
favorable conditions for infection but removes the protecting 
spray. 



PEAR 



536 



Fire-blight, blight '^^~'^^' ^^^ {Bacillus amylovorus (Burr.) 
Trev.). — The name ''fire-blight" is well chosen, since the 
affected tree,, with its shriveled branches and shrunken, 
blackened twigs, gives the impression of fire injury. During 
the winter diseased twigs may be recognized by the dead, 
shriveled leaves still clinging to them. In the early spring, 
these leaves still persist, while on closer examination the 
bark and wood of the blighted twigs are seen to be black 
and dead. This blight is the most important disease of 
the pear and is also serious on the apple, quince, and haw- 
thorn, and to some extent it affects plum, apricot, and 
mountain ash. 



Pomaceous Fruits 



63 



Fire-blight was first described in 1794 from the Hudson 
Valley, whence it spread in every direction, reaching Califor- 
nia about 1900. In many cases even whole orchards have 




Fig. 30. — Fire-blight; healthy and diseased twigs. 
Original. 

succumbed to its attack. One pear grower near Washing- 
ton, D. C, estimated his loss from this one disease in one 
year at $10,000. It is as yet confined to North America and 
is more severe in the Southern than in the Northern states. 



64 Diseases of Economic Plants 

So diverse and numerous were the early theories as to the 
nature and cause of bhght, and so fruitless were the discus- 
sions in earlier years that the Western New York Horticul- 
tural Society passed resolutions to prohibit further reference 
to the subject until entirely new facts were forthcoming. 
Among the numerous theories may be mentioned those 
depending upon electrical or atmospherical influences, 
freezing of the bark, too long culture of particular varieties, 
freezing of the roots, too high culture, insects, fungi, and 
lack of nutrition. One of the most prominent of these was 
Downing's ''frozen sap theory," according to which the 
disease is due to the freezing and thawing of the sap, resulting 
in loss of vitality and development of poisons in the tissues. 
It is unnecessary to discuss any of these theories further than 
to say that none of them explains the facts. 

In 1878 Burrill discovered bacteria in the diseased twigs, 
and by transferring to healthy twigs some of the exudate 
from diseased tissue bearing these bacteria was able to 
cause the disease. Arthur later grew the bacteria in pure 
cultures and with these cultures produced the disease. It 
was thus proved beyond question that bacteria cause the 
blight. 

It has been demonstrated that the germs cannot gain 
access through healthy, mature bark, but will readily pene- 
trate into wounds, or into floral parts. 

This blight bacillus deposited upon the flower, or upon 
tender shoots, gains entrance and rapidly grows downward 
through the wood and bark, causing the foliage upon the 
affected twig to die. The disease rarely progresses more 
than 5-8 cm. in one day, though even 0.3 meter is occasionally 
reached. Ordinarily, sick twigs dry out, progress of the 
disease soon stops, and the germs in the twig die. Waite 
found that in some limbs, probably one of several hundred, 
the disease remains active. Two forms of blight are thus 
distinguished : one very dangerous, the other no longer offen- 
sive. It is the limbs still in condition of "active blight" that 
carry the pest over winter. 



Poraaceous Fruits 



65 



With the flow of sap in the spring these infested hmbs 
exude a milky fluid teeming with the bacteria and thus be- 
come centers of reproduction. It has been demonstrated that 
several species of insects can carry infection, but it is not 
probable that they are really important agents of transmis- 
sion/^ Two additional forms of this disease, according to the 
part affected, are recognized: (1) blossom-blight, (2) body- 
blight and canker. 

Neither of these differs essentially from twig-blight, 
though body-blight or canker is especially worthy of men- 
tion on account of its pecul- 
iar destructiveness. This 
form occurs where infection 
is led by a spur, shoot, or 
sucker, or where the germ 
enters through a wound 
into the body or main limbs 
of the tree. The result is a 
canker more or less cir- 
cular, which may even 
girdle the tree or branch, 
and which in any event 
causes serious injury. 

The susceptibility of the tree is largely influenced by ex- 
ternal conditions. In general, anything that leads to rapid 
growth, resulting in tender shoots, favors the development of 
the disease. There is also much difference in resistance 
offered by different varieties. The Anjou, Kieffer, An- 
gouleme, and Seckel possess more resistance than the Bartlett, 
Clapp, or Flemish Beauty. 

Based on the facts as stated above, the following sugges 
tions for avoiding the blight were deduced, and tested b\ 
Waite. 

1. Pruning in winter when the tree is dormant promotes 
growth and favors blight. Withholding the pruning knife, 
which may not otherwise be best for the tree, will reduce 
this tendency. 




Fig. 31. — Fire-blight showing exu- 
date from bark, much enlarged. 
This teems with the causal bac- 
teria. After Whetzel. 



66 Diseases of Economic Plants 

2. Overstimulation with fertilizers, especially those rich 
in nitrogen, is to be avoided. 

3. A well-cultivated tree is more inclined to blight than 
one growing on sod or untilled land. 

4. In irrigated orchards a reduction of the water supply 
to the minimum has been found effective. 

In nurseries or small orchards or in regions where the 
blight is not excessive, the disease may be reduced by cutting 
out and burning every particle of blight when the trees are 
dormant. Not a single case of blight should be allowed to 
survive the winter, either in the orchard or within half a 
mile of it. Every pomaceous tree near by, including the 
apple, pear, quince, Siberian crab apple, wild crab apple, 
the mountain ash, service berry, and all the species of Cratae- 
gus, or hawthorns, should be examined for this purpose, the 
blight being the same in all. The orchardist should not stop 
short of absolute extermination in every case, for a few trees 
or branches overlooked may go a long way toward undoing 
all of his work. Cutting out the blight may be done at any 
time in the winter or spring up to the period when growth 
begins. The best time, however, is undoubtedly in the 
fall, when the foliage is still on the trees and the contrast 
between the blighted *and the healthy limbs is strong. It 
is further necessary to make a weekly inspection of every 
tree throughout the growing season, beginning when the 
blossoms fall, in order to cut out blight whenever it is 
found. 

In each case it is essential to cut well below any external 
evidences of the disease. To avoid spreading the infec- 
tion, in case the pruning tools should accidentally cut into 
the diseased tissue, the cutting blade should each time be 
disinfected by wiping it with a cloth saturated with a strong 
solution of corrosive sublimate (1 part to 1000). When the 
wound made by this excision is at all large, it also should be 
disinfected with the corrosive-sublimate solution. Particular 
care should be taken to remove and burn all diseased spurs 
and water sprouts. 



Pomaceous Fruits 67 

Unless continued, careful inspection is given, and concerted 
action in a community maintained, but little benefit will 
follow. 

Rust ^^' ^^' ^^^ (Gymnosporangium sps., Roestelia). — Rust 
of pear is very similar in nature to rust of the apple, though 
less often injurious. It consists of a summer stage and a 
winter stage. The former produces rust on the leaves of the 
pear, while the winter stage of the eastern form of rust pro- 





FiG. 32. — Scab on California pears bought in Raleigh, N. C, 

Original. 

duces the familiar cedar-apple upon the cedar tree. The pear 
rust of the West is a distinct species, with the incense cedar 
as the alternate host. 

The remedy, as in the case of the apple, consists in re- 
moving all red cedar trees from the neighborhood of the 
pear orchard; thus eliminating the source of infection. 
When this is impossible, the pear trees should be sprayed 
with Bordeaux mixture immediately after the early rains 
which cause the gelatinous horns to emerge on the cedar- 
apple, and thus furnish the supply of spores for the spring 
infection. This disease of pears is particularly abundant 
upon varieties of the Japanese strain. 

Powdery-mildews. See apple. 



68 



Diseases of Economic Plants 



Scab ^^' '^^ (Venturia pyrina Aderh., Fusicladium) . — This 
scab much resembles that of the apple and is often accom- 
panied by a peculiar cracked appearance of the skin. This 
symptom, however, is secondary and is not necessarily 
present. Rough cankers are formed upon the twigs. Pear 

scab is generally distributed 
throughout the United States 
and Europe. 

The use of a dormant 
spray followed by two appli- 
cations of Bordeaux mixture, 
while the buds are unfolding, 
is recommended. 

Leaf-spot "^^ {Mycosphce- 
rella sentina (Fr.) Schr., Sep- 
toria). — Leaf -spot, while 
rarely completely destructive 
to foliage or crop, does inter- 
fere with the general pro- 
ductiveness and health of the 
tree by diminishing its green 
surface, often causing defoli- 
ation. It is known over a 
wide range and is common, 
especially in the Eastern 
United States and in Europe. 
Leaf-spot may be distin- 
guished from scab and blight 
by the fact that the diseased area is rather sharply defined 
and characteristically angular in outline. The center of the 
spot, usually ashen in color, is surrounded by a narrow brown 
zone, and this in turn by one of purplish hue. The ashen 
center bears several minute, dark-colored pycnidia. 

The treatment recommended for pear scab is preventive. 

Leaf -blight ^^ {Fabrcea maculata (Lev.) Atk., Entomos- 

porium). — This leaf-blight, more serious than leaf -spot, is 

almost as widely distributed as is the pear itself, though 




Fig. 33. — Pear leaf-spot. After 
Anderson. 



Pomaceous Fruits 69 

less prevalent in the South and West than in the North 
and East. 

The entire leaf area often presents a diseased appearance, 
and there is no striking zonal arrangement in the infected 
spots as in leaf -spot. Eventually the leaf yellows, or turns 
brown and falls. The blight may attack the fruit itself, caus- 
ing a red spot, which in a later stage resembles pear scab. 

The treatment already recommended for pear scab will 
suffice for pear leaf-blight. 

Black-rot canker (Physalospora cydonice, Sphceropsis.). — ■ 
In appearance and treatment this disease is similar to black- 
rot of the apple. 

Minor diseases 

Pink-rot often follows scab. The cause and general rela- 
tions are given under apple; Bark-canker, Frost injury, 
Crown-gall, Sooty-blotch, Fly-speck, Black-mold, Brown- 
rot, Texas root-rot, Hypochnose, Septobasidium canker, 
Die-back canker, Altemaria, see apple. Bitter-rot is 
identical with that of the apple but is of slight importance 
on the pear. Red-leaf, a disease of unknown cause, has been 
noted in New York. 

QUINCE.so 

Rust ^^' "^^^ ^'^^ {Gymnosporangium clavipes C. & P., Roes- 
telia) . — The quince rust, spring stage, agrees with apple 
rust in general characters. The causal fungus grows upon 
the fruit in the summer and produces there myriads of spores 
which, on the approach of fall, are carried by the wind to ad- 
jacent red cedar trees (Juniperus), and there produce swellings 
upon the branches and twigs during the fall and winter. In 
the spring, these give origin to masses of spores embedded in a 
matrix of jelly. These spores are conveyed to the quince tree 
by the wind, and there again produce the quince rust. The 
cedar is a necessary resting place for this fungus durmg 
the winter. 



70 



Diseases of Economic Plants 



The remedy, therefore, if practicable, is to remove the 
cedar trees from the neighborhood of quince trees. This will 
almost entirely prevent the rust, although in rare instances 
a few spores may be carried a considerable distance. In 
case the cedar is too abundant to permit of its complete 
removal, resort must be had to spraying the leaves and 
fruit of the quince trees with Bordeaux mixture at the 




Fig. 34. — Young quinces showing rust. After Bailey. 

time when the rust spores are expected to arrive; that is, 
at the time when the gelatinous spore masses are present on 
the cedar-apple. 

Blight {Bacillus amylovorus) . — This disease has been 
sufficiently discussed in connection with the pear and apple. 
It is only necessary here to indicate that it is the most serious 
known disease of the quince. The treatment is the same 
as that recommended for this disease on other pomaceous 
trees. 

Leaf-blight, black-spot ^^ (Fabroea maculata (Lev.) Atk., 
Entomosporimn) . — Both the fruit and foliage are affected 



Pomaceous Fruits 71 

by this blight, the foUage spotting and faUing prematurely 
so that the vitality and vigor of the tree is much reduced. 
Upon the fruit it causes black blotches, first seen as small 
brown spots, which soon increase in size and turn darker 




Fig. 35. — Black-spot of the quince, natural size. After Bailey. 

in color. While this spot does not materially injure the 
fruit for use, it does retard its full development, and, be- 
cause of impaired beauty, decreases its selling price. It also, 
as in the case of apple scab, gives entrance to the pink-rot 
fungus. 

The means of prevention consists in application of lime- 



72 Diseases of Economic Plants 

sulfur. P^epeated trials have shown that this is thoroughly 
effective, increasing the value of the quince crop very mate- 
rially both in size and quality of the fruit. The first applica- 
tion should be made soon after the blossoms fall, and should 
be followed at intervals of two or three weeks with two more 
treatments. 

Black-rot {Physalospora cydofiice, Sphceropsis) . — This 
rot of wide distribution, and often amounting to a loss of 
10 per cent, is due to the same fungus which causes black-rot 
of the apple, and the treatments recommended for the apple 
will prove efficient for the quince disease. It has not yet been 
proved that this fungus causes cankers on the quince trees 
such as have been described for the apple. The grower 
should, however, watch carefully for the presence of canker, 
as the relation between the canker and the rot in apple indi- 
cates that the canker may possibly be found on the quince 
also. 

Bitter-rot (Glomerella cingulata, Gloeosporium) . — This 
disease is caused by a fungus identical with that causing 
bitter-rot of the apple. The treatments already recom- 
mended for other diseases will also prove efficient here. 

European canker (Nedria galligena Bres.). — This canker 
is readily distinguished from the ordinary cankers pro- 
duced by Physalospora or Glomerella by its brilliant red or 
cinnamon-colored pustules scattered profusely over the 
affected areas. While cankers due to this fungus have been 
observed upon quince in America, no case of serious injury 
is known. 

Pale-rot (Phoma cydonice S. & S.). — This is one of the 
most prevalent decays of quince fruit in market. The 
lesions usually appear in the region of bruises and are at first 
pale blue or bluish-green in color and circular in outline. The 
rot spreads rapidly, involving the entire fruit in a few days. 
The surface becomes wrinkled and darker in color. Later 
numerous white fruiting pustules stud the surface of the 
decayed area. Care in handling the fruit to avoid external 
injuries is the only control measure recommended. 



Pomaceous Fruits 73 

Minor diseases 

Brown-rot, Crown-gall, and Hypochnose : see apple. 

MEDLAR 

Though not extensively cultivated the medlar is occa- 
sionally affected with fungi allied to those present on other 
pomaceous hosts, e. g. Fahrcea mespili (Sor.) Atk. causing 
leaf-blight; Oidiwn tnespilinum Thiim, and Sclerotinia lin- 
hartiana. P. & D. 



DRUPACEOUS FRUITS 28 

The drupes as the pomes, comprising highly valuable 
individual trees, warrant protective, curative, even though 
expensive measures. The diseases of the drupes, to some 
extent, are identical with those of the pomes, since both 
belong to the Rosaceae. There are, however, several im- 
portant diseases peculiar to this group of hosts. The drupes 
are especially sensitive to injury by fungicides, a fact which 
complicates all questions of control of drupe diseases by 
spraying. 

ALMOND 

The chief diseases: Yellows, Blight, Crown-gall, and 
Shot-hole are discussed under peach. 

APRICOT 

The diseases of the apricot are essentially those of the 
peach and will be more fully discussed under that head. 
The most important are : Yellows, less common than on the 
peach; Phyllosticta Shot-hole; Brown-rot, especially destruc- 
tive in the southwest; Fire-blight (Bacillus amylovorus), 
rarely reported^-; Scab, reported from California, Texas, 
and Connecticut; Die-back (Valsa leucostoma); Crown-gall; 
Black-spot {Pseiidomonas pru7ii) , less troublesome than on the 
peach; Silver-leaf; Rust, especially injurious in the South- 
west; Coryneum blight,^^ known in California, New York, 
Australia, and northern Africa; Frost injury. Gummosis is 
not a specific disease but a symptom brought about by any 
one of various agencies; see peach. 

74 



Drupaceous Fruits 75 



CHERRY 



Leaf-spot ^' ^^~^^ (Coccomyces sps., Cylindrosporium) . — 
The disease, first reported in Europe in 1884, is widespread 
wherever cherries are cultivated and is usually very destruc- 
tive. Sweet cherries are most susceptible. In Ohio the loss 
in one year was estimated at $25,000. This disease, on fruit, 
pedicels, and leaves is nearly identical in symptoms with 
that of leaf -spot of the plum. For description see p. 98. 
Diseased refuse, leaves, etc., should be plowed under or 
destroyed. Sour cherry trees should be sprayed with lime- 
sulfur solution diluted at the rate of IJ^ gallons to 50 gallons 
of water, or with 3-4-50 Bordeaux mixture: (1) as soon as the 
petals have fallen, (2) about three weeks later, (3) directly 
after the fruit is picked. Arsenate of lead, 1 pound of powder 
to 50 gallons of spray, may be added for the control of insect 
pests. 

Sweet cherries should receive the same treatment as the 
sour except that lime-sulfur solution diluted at the rate of 
1 gallon to 50 gallons of water should be the fungicide used. 
Bordeaux mixture should never be used on sweet cherry 
trees, because of the risk of injury. Dusting has proved 
satisfactory in some localities. The results of spraying by 
Scott are shown in the accompanying figures. These trees, 
located in Illinois, were spra3^ed three times. 

Black-knot (Dihotryon rnorhosum). — As upon the plum, 
this knot causes serious injury to the cherry. In some 
sections it is so prevalent on the wild cherry and plum 
trees as to rendei* control practically impossible, and in 
certain regions has caused the abandonment of the cherry- 
growing industry. Taken in time it is easy to control. For 
treatment see plum. 

Brown-rot, mold {Sclerotinia dnerea, Monilid) . — The 
same fungus which produces disastrous results upon the 
peach also causes the most serious disease of the cherry, being 
especially destructive on sweet cherries. Several stages of 
its development are illustrated in Fig. 38. The disease is 





^ A 


V^rSv 


-»,-*' 




J'X ^4-^?*, 


i 


-y.^-;r^^^?. ^.,^ 




"^'5^^^ 


^^^wj^^^^^'*"' ; 






^ 




L^ 


-V'/^ 


kf/^ 


^^^Ppfm '^^^"^■•™fflH^te^ 






g^^^N,S. 


^''^^^^^^^^^"' JHHMn 






- 


'ilM 



Fig. 36. — Unsprayed cherry tree defoliated by leaf-spot. After Scott. 



i^ '1^' 


% 


^^^^K^^-'^-''''--^^i-'y 


mr-. 







Fig. 37. — Cherry tree from same orchard shown in Fig. 36, sprayed 
with self-boiled lime-sulfur to control leaf-spot. After Scott. 



Drupaceous Fruits 



77 



known practically wherever the cherry is grown, and large 
losses are frequent. Fifty per cent loss was reported from 
New York, and 25 per cent from Missouri in a single year. 
Treatment is the same as for the peach brown-rot. 

Curl {Taphrina cerasi (Fcl.) Sad.). — Cherry curl is 
closely related to that of the peach. The leaves become 
wrinkled before they are full size, and spores are produced on 




Fig. 38. — Brown-rot showing various stages of decay, x'^fter Clinton. 

the surface of the leaf, as they are in other curls. Instead of 
forming flower buds and spurs, affected regions develop a 
profusion of twigs, ^'witches' brooms." The disease is not 
common in America; but should it become so, it can be held 
in check by pruning out the diseased twigs. It is perennial 
in the twigs and should be avoided in budding and grafting. 
Powdery-mildew ^^' ^"^ {Podosphcera oxyacanthce (DC.) De 
Bary) . — This mildew, similar to that described in connec- 
tion with apple diseases, sometimes does damage to the 
plum and cherry, especially on nursery stock, where it pre- 



78 



Diseases of Economic Plants 



vents either the growth of the seedUng or successful budding 
or grafting. 

On old leaves, though often abundant, the fungus does not 
cause great damage, but when the attack is made on young 
growing tips, or on young leaves, these delicate structures 
suffer greatly from loss of nourishment. The disease is com- 
mon from the Atlantic to the Pacific. 

Unlike most fungi the mildew grows best during fair, 
dry weather. A light rain, which spreads the spores and 

furnishes sufficient moisture for germi- 
nation, followed by a dry spell, best 
favors the development of powdery- 
mildew. 

The use of Bordeaux mixture, sulfur 
dust, or lime-sulfur has proved satisfac- 
tory. Apply about every ten days dur- 
ing the early growing season; more 
frequently, if necessary to replace the 
poison washed off by rain. 

Wood-rot ^^ {Schizophyllum alneum 
(L.) Schr.). — Small white specks, the 
sporophores, appear upon the limbs 
and trunk in early summer. In the 
autumn they are well developed and 
abundant; white and very hairy, 1-3 cm. 
in diameter, usually attached on one 
side with the margins incurved. The 
gills are white, woolly, branched, deeply 
split along the edge, and revolute. 
The affected wood is brittle and pene- 
trated by black lines. Apparently this disease starts in roots 
injured by tools during cultivation or in wounds upon limbs. 




Fig. 39. — Schizo- 
phyllum alneum, 
frequently the 
causal fungus of 
wood-rot of cherry 
and other trees. 
After Atkinson. 



Minor diseases 

Die-back ^^ (Valsa leucostoma, Cystospora). — The discus- 
sion of die-back on p. 86 is applicable in this connection. 
The disease is common on the cherry in the United States 



Drupaceous Fruits 



79 



and other countries. For Crown-gall, Rust, and Yellows, 
see peach. Armillaria root-rot, see apple. Blight {Bacillus 
amylovorus) has been rarely reported in the Northwest. 
Scab is much less common than on the peach. Black-spot 
(Pseudomonas pnmi) has been noted on the Wragg cherry in 
Colorado. See peach. 



PEACH 

Brown-rot ^^' ^^' ^^ {Sclerotinia cinerea (Bon.) Schr., Mon- 
ilia), — Probably no other disease is so destructive to 




Fig. 40. — Two packages of peaches, one healthy, the other affected 
with brown-rot. After Scott. 

peaches, plums, cherries, and kindred drupes, as the brown- 
rot, which attacks the fruits as they approach maturity, 



80 



Diseases of Economic Plants 



turning them brown, soft, and rendering them worthless. 
Aside from injuring the mature fruit, the rot attacks the 
flowers and twigs. The disease ranges over the entire peach- 
growing territory, but is usually most severe in the South. 
In some years the loss has amounted to more than 50 per cent 
of the crop, or an aggregate annual loss of $5,000,000. The 
estimated damage in Ohio alone in one year was a quarter 
of a million dollars; in one year in Pennsylvania twenty 
carloads were lost. Apples, pears, and quinces are attacked, 
but to lesser extent. 

Its characteristic appearance on the fruit enables one to 
recognize it easily. It fir^t appears as small, circular, brown, 

decayed spots. These rapidly en- 
large until they embrace the 
whole fruit, which at the same 
time shrinks slightly. As the 
decay advances, small tufts of 
brown threads appear near the 
centers of the original spots, and 
spread rapidly until the whole 
fruit is covered. 

If the fruit hangs in clusters, 
adjacent fruits begin to decay at 
the points of contact, and the dis- 
ease spreads from fruit to fruit un- 
til whole clusters are lost. Fruit, 
after it is picked, may also suc- 
cumb to attack, and peaches that 
were apparently sound at picking may be seriously damaged 
when they reach market. Thus the loss falls upon grower, car- 
rier, dealer, and consumer. The decay is so rapid that infection 
to-day may mean a totally unsalable peach two days hence. 
Peaches diseased on the tree may fall to the ground, or remain 
on the tree, where they shrivel and hang over winter, to con- 
stitute the ''mummy" peaches so familiar in infected orchards. 
Upon the blossom the disease is first evident as a slight, 
brownish discoloration, which spreads rapidly, causing the 




Fig. 41. — Mummy peach 
showing Sclerotinia asco- 
phores. After Scott. 



Drupaceous Fruits 81 

flower to wither and eventually fall off as a rotten mass, 
carrying contagion to everything in its path. This damage 
to the flower is often confounded with frost effects. From 
the flower the rot may spread to adjacent twigs, through 
the flower stalk. Smith states that the examination of hun- 
dreds of twigs in all stages of disease showed that every one 
was associated with blighted and persistent flowers. Infec- 
tion of the twigs may also occur directly from diseased fruit. 
Even large branches may become seriously cankered. From 
repeated observations, however, it seems probable that 
branches cannot be infected except through wounds. 

The inroads of this disease are so serious that many peach 
and plum growers have been obliged either to secure a 
remedy for this pest or abandon the crop. Years in which 
there is full fruitage, accompanied by damp, warm weather, 
are almost certain to bring a severe attack. But it is not the 
weather which directly causes the rot; rather it is the rapid 
development of the fungus under proper weather conditions. 

The mummified fruits and cankers serve as the hibernating 
quarters of the causal fungus. If these mummies be carefully 
observed in the spring, some of them will be seen to bear 
small stalked disks (Fig. 41). These are the organs which 
furnish spores for the spring infection. 

It follows that any practice which destroys the mummified 
fruits lessens the risk of infection as does also the pruning 
out of cankers. Observations by Pollock, ^^^ extended over a 
period from 1909 to 1918, show that the sclerotia of the 
causal fungus may remain alive for at least ten years, and 
some of them produce ascocarps every year; old mummies 
or fragments of mummies giving rise to smaller spore- 
bearing structures than those formed from younger sclerotia. 
In the light of these observations attesting to the long life 
of the sclerotia, the plowing under of diseased fruits, here- 
tofore advised, cannot be regarded as a good practice. Ac- 
tive treatment in the form of spraying is necessary. The most 
successful spray is that employed by Scott, which gave the 
following results : — 



82 



Diseases of Economic Plants 



Results of Experiments for the Control of the Peach Brown- 
Rot, Marsha LLViLLE, Ga., 1908 







Peaches 




Peaches 


Plot 


Treatment 


affected with 


Peaches 


BADLY 






Brown-Rot 


Scabbed 


Scabbed 






Per cent 


Per cent 


Per cent 


1 


Lime-sulfur wash (15-10- 










50), hot water 


10.56 


20.75 


0.80 


18 


Lime-sulfur wash (15-10- 










50), cold water 


12.22 


16.60 


0.60 


36 


Check — no treatment. . . 


36.98 


93.63 


42.12 



For the combined treatment of peach scab and brown-rot, 
at least three appUcations of the self-boiled lime-sulfur, 
8-8-50, are necessary; first, when the petals drop; second, 
about three weeks later; third, about a month before the 
fruit ripens. The time of the last application must be deter- 
mined by the ripening date of the variety. Though a late 
treatment would be effective against brown-rot, to avoid 
staining the fruit the last spraying should be made a month 
before the fruit ripens. Three applications are sufficient for 
the Elberta and earlier varieties. A fourth treatment is 
often desirable for later maturing varieties. 

There seems to be no question as to the advisability of 
spraying the peach orchard where brown-rot and scab are 
troublesome, but other risks are oftentimes to be encoun- 
tered. The curculio and other insects readily break the skin 
of the peach and admit the brown-rot fungus even through a 
coating of the spray mixture, so that a certain amount of rot 
may always be expected when the conditions are favorable. 

Scab ^^' ^^ (Cladosporium carpophilum Thiim.). — This 
disease, which is widespread and so common that many 
people regard it as an integral part of the peach, may con- 
sist of isolated, sooty, black specks, or of black specks so 
numerous as to coalesce into large blotches. These some- 
times cover as much as one-third or one-half of the peach. 



Drupaceous Fruits 



83 



The side which is attacked is dwarfed, often cracked, and 
the flesh adjacent to the diseased part is green and bitter, 
even after the normal portions are ripe. Leaves and twigs 
are also affected. 




Fig. 42. — Peach scab. Original. 



Scab develops in most serious form during rainy seasons, 
and is more prevalent upon certain late varieties as Health, 
Salway, and Bilgen. It is reported from Missouri to have 
done damage equal to 70 per cent of the value of the crop, 
and Selby estimated the loss in one crop in Ohio at from 20 to 
50 per cent. 



84 



Diseases of Economic Plants 



Self-boiled lime-sulfur, 8-8-50, applied as indicated for 
peach brown-rot, gives excellent results. 

Curl ^^ {Taphrina deformans (Fcl.) Tul.).* — Throughout 
the peach-producing region this disease abounds, being par- 
ticularly injurious in moist localities. The annual loss 
approximates $3,000,000 in the United States. 

Curl is due to a fungus which grows in the leaves, causing 
the peculiar malformation which justly gives rise to its 



J 


^"V- 


^ 


/ 




F 


y^ 


^SH^^BH 





Fig. 43. — Peach leaf-curl. After Atkinson. 



popular name. This fungus destroys the utility of the leaf 
as a starch-producing organ, and eventually causes defolia- 
tion. This loss may be manifest in two ways: first, by the 
present effect upon the vitality and vigor of the tree, and 
immediate injury to the crop; second, by a weakening of the 
tree in succeeding years, due to the lack of full nourishment 

* The sub-genus Exoascus is by some regarded as of specific rank and 
the name as Exoascus deformans. 



Drupaceous Fruits 85 

during the period of attack. The injury in the present year, 
manifest by a loss in productiveness, is obvious to the grower. 
The injury in succeeding years, often fully as great, is fre- 
quently overlooked, or is not attributed to its true cause. 

It was formerly thought that this fungus persisted in the 
twigs over winter, and thus lurked ready to infect the new 
leaves as they began to develop. It has, however, been 
proved that nearly, if not quite, all spring infection is due, 
not to perennial mycelium, but to spores which remain on 
the bark of the trees. 

Prevention of the disorder lies in killing these spores of 
the fungus by winter spraying. For this purpose Bordeaux 
mixture, lime-sulfur, or a simple copper-sulfate solution 
is efficient. There is probably little choice between these 
solutions on the ground of efficiency; hence, the cost of the 
various sprays may become the deciding factor. Lime- 
sulfur is preferable when insects also are to be met. The 
spray should be applied from one to three weeks before the 
buds open in the spring, and thoroughness should be the 
chief aim. Spraying should be done in dry, calm weather, 
during the middle of the day, in order to avoid dew or frost 
upon the limbs. 

Pierce states that as a result of the treatment of peach 
curl in California, from 95 to 98 per cent of the spring 
foliage was saved. A net gain of 600 per cent in the foliage 
over that retained by adjoining unsprayed trees resulted 
in the case of several different sprays. Bordeaux mixture, 
when applied to the dormant tree, increased the weight and 
starch-producing power of the leaves, and the sprayed trees 
showed great gain over the unsprayed in the number and 
quality of the fruit buds which they produced for the follow- 
ing year. The gain in the number of spur buds was over 
100 per cent in some cases. The sprayed trees also produced 
more vigorous growth of new wood, the wood to produce the 
crop for the next year. Thus, in one experiment the spring 
growth of the unsprayed tree averaged 7.85 inches; on the 
sprayed trees it was 24.75 inches. The average value of 



86 Diseases of Economic Plants 

fruit, per tree, in rows treated with the most effective Bor- 
deaux mixture ranged as high as $6.20 above that in ad- 
joining untreated rows, or the equivalent of a net gain of 
$427.80 per acre. Over one thousand per cent net gain in the 
set fruit has resulted from the use of some of the more effec- 
tive sprays. 

The trees should be sprayed each season, since experi- 
ments prove that treatment one season will not prevent the 
disease the following year. Spraying should be done even 
though the trees are not expected to bear, since the loss of 
the crop of leaves is as great a drain upon the trees as is the 
maturing of one-half to two-thirds of a crop of fruit. 

Die-back'-'^ (Vaha leucostoma (Pers.) Fr., Cytospora). — 
This disease of limbs, trunk, and twigs was first fully de- 
scribed in the United States by Rolfs of Missouri in 1907 who 
noted it upon peach and Japanese plum. It is present also in 
Europe and Australia. 

Infection occurs upon buds or wounds during the growing 
season, and in early winter and spring the tips of young 
branches, especially water sprouts, are killed back from 2.5 
to 46 cm. As many as 300 such dead twigs have been noted 
on a single tree. It develops most rapidly in a warm spell 
following freezing weather in the spring, and is more serious 
upon trees that have been weakened by other causes. 

Twigs killed during the winter show at first a dark pur- 
pHsh skin, changing later to leathery, scarlet, or purple, 
finally drab. Then the skin loosens and wrinkles. At this 
time black pycnidia appear under the skin. These soon 
push out a white cap through a transverse slit in the skin, 
and in wet weather exude very fine, red threads of spores. 
Gum flow usually accompanies the constriction, marking 
the juncture of dead and healthy wood. During summer, 
leaves on infected twigs frequently wilt, owing to the gir- 
dling of the stem. Upon the trunk large wounds, often 
regarded as sun scald, are produced, while upon young limbs 
the wounds appear as enlargements or ''knots." Large 
limbs or even whole trees succumb. 



Drupaceous Fruits 87 

Excision should be practiced. Spraying lessens the disease 
but is not wholly effective. 

Coryneum-blight ^^' ^^ {Coryneum beijerinckii Oud.). ^ — 
First noted by Pierce and fully described by Smith, Cory- 
neum-blight, troublesome in California for years, has been 
observed as far east as New York, also in Europe and Aus- 
tralia. 

The symptoms are dying of the buds of fruiting wood, 
spotting of green twigs, and dropping or underdevelopment 
of young leaves and fruit, accompanied by gummy exudate, 
especially upon the one-year-old fruiting twigs. Leaves 
opening from buds which survive the disease are marked by 
small dead areas of tissue, which soon fall out, leaving ^'shot 
holes." It is essentially a winter or early spring disease of 
fruiting twigs and one-year-old wood, and the principal dam- 
age is from death of buds and twigs before the fruit de- 
velops. Infection occurs in winter before new growth begins. 

Pruning, followed by spraying with Bordeaux mixture or 
other dormant sprays, during the early winter (in California 
between November 1 and December 15), produces best 
results. 

Crown-gall and Hairy-root ^^ ^^''^' ''~^ {Pseudomonas tume- 
faciens EFS.). — Crown-gall causes a tumor-like outgrowth 
near the ground line on certain trees and shrubs (Fig. 44), 
particularly upon members of the rose family, pomes, drupes, 
raspberries, etc. Hairy-root consists of a profuse develop- 
ment of small tufts of fine roots. 

Careful cross inoculations by Hedgcock, using fragments 
of galls, have demonstrated that crown-gall of the almond, 
apricot, blackberry, cherry, peach, plum, prune, chestnut, 
and walnut are intercommunicable. It has also been demon- 
strated by Smith and Townsend that crown-gall of the peach 
tree as well as of tomato, potato, tobacco, beet, hop, carna- 
tion, grape, raspberry, and apple can be produced by inocula- 
tion with Pseudomonas tumefacieris, also that the organisms 
of the peach, apple, hop, rose, and chestnut galls are inter- 
changeable. 



88 



Diseases of Economic Plants 



In addition to the above-named plants, natural galls on 
quince, plum, dewberry, raspberry, corn, turnip, salsify, 
parsnip, lettuce, radish, cotton, alfalfa, clover, pecan, willow. 




Fig, 44. — Peach crown-gall. After Hedgcock. 

poplar, chrysanthemum, honeysuckle, euonymus, arbutus, 
marigold, pyrethrum, peony, and oleander have been studied, 
while a complete list of susceptible plants would include 
many more. The disease in a form known as soft-gall is 
found commonly on herbaceous plants or cane fruits. 



Drupaceous Fruits 



89 



On many plants crown-gall is practically harmless, while 
on others, especially the fruit and nut trees and the cane 
fruits, it is injurious. The chief injury seems to arise from 
the fact that crown-gall paves the way for the entrance of 
rot-producing parasites, interferes with proper root develop- 
ment and the conduction of foods and water. Whatever 




Fig. 45. — Cracked peach, caused by Pseudomonas 
pruni. Advanced stage on fruit nearly ripe. 
After Roberts. 

may be the actual mode of producing injury, the fact is well 
estabhshed that trees with crown-gall do not, in general, 
develop or yield as well as trees without galls, though in rare 
cases, trees with crown-gall may fully equal ungalled trees. 
All diseased stock should be avoided, as well as stock from 
nurseries where the disease is known to exist. Care on the 
part of nurserymen to use soil free from crown-gall; to avoid 
wounding the young trees and to make close-fitting grafts, 
and protect them well with wax, will lessen infection. 



90 



Diseases of Economic Plants 



Black-spot ^^^"^^^ {Pseudomonas pruni EFS.). — Pep.ches, 
plums, apricots, nectarines, and more rarely cherries are 




i*'iG. 46. — ■ Peach leaves inoculated with culture of Paeudomonas pruni. 
Photograph taken 43 days after inoculation. After Eolfs. 



susceptible to black-spot, affecting chiefly the leaves, but 
occurring, also, on fruit and branch. It constitutes a really 
serious disease on peaches, being next in importance to 



Drupaceous Fruits 91 

brown-rot and scab, and occurs in the Eastern and Central 
United States, though unknown outside of the United States. 
It was first noted about 1903. 

Spots first appear on the leaves as small, gray specks which 
soon become angular and water-soaked, later brown. Single 
spots measure 1-5 mm. in diameter. The diseased tissue 
usually drops out, leaving ''shot-holes." Badly diseased 
leaves fall and a large percentage of defoliation is common. 
On twigs, water-soaked spots surrounding the lenticels 
appear, developing to a length of four centimeters or more. 
The diseased areas become sunken and brown in age, and 
often develop into perennial cankers. On fruit, the specks 
are at first similar to those on the leaves, but the skin soon 
breaks and cracks appear. (Fig. 45.) 

Trees that are kept in good growing condition by proper 
pruning and cultivation are not seriously injured by black- 
spot. 

Powdery-mildew {Podosphcera oxyacanthce (DC.) De Bary, 
and Sphcerotheca pannosa (Wallr.) Lev.). — These wide- 
spread mildews, in general appearance, are similar to the 
powdery-mildew of the grape, cherry, lilac, and rose. Some- 
times the attack is so general, on twig, leaf, and fruit as to 
practically destroy the crop. When on fruit, the mildew ap- 
pears first while the peach is small, causing irregular, grayish, 
moldy blotches. As these enlarge, cracks often develop. 

Sulfur may be used as a dust, or a lime-sulfur spray, 1-50, 
may be applied. Treatment should be made as soon as the 
mildew is seen. Two or three treatments may be required. 

Yellows. ^^^' ^^^' ^^- — Peach yellows has been known in the 
United States since 1760. From a region near Philadelphia, 
as a center, it has spread until now it is known throughout a 
large territory embracing Virginia, Arkansas, Texas, and 
Canada, and is constantly extending its frontier in every 
direction. It is not known to occur outside of North America. 
The disease is of unknown origin, but it has been proved 
beyond question that it is contagious. The roots of diseased 
plants, however, do not infect the soil, and trees may safely 




92 Diseases of Economic Plants 

be set in the places from which diseased trees have been 
removed. 

Recognition marks, which leave no uncertainty as to its 
identity, are described by Smith as follows:^ 'Prematurely 
ripe, red-spotted fruits, and premature unfolding of the 
leaf buds into slender, pale shoots, or into branched, broom- 
like growths, are the most characteristic 
symptoms of yellows. The time of ripen- 
ing of premature fruit varies within wide 
limits; sometimes it precedes the nor- 
mal ripening by only a few days, and at 
other times by several weeks. The red 
spots occur in the flesh as well as on the 
skin, making the peach more highly col- 
ored than is natural. The taste of the 

t? /IT ' Tv/rij fruit is generally inferior and often in- 
FiG. 47. — Mildew ... , • , , • r^n i • 

upon peach fruit, sipid, mawkish, or bitter. Often this 

After Bailey. premature ripening is the first symptom 

of yellows. The peaches are then of good 

size and quite showy, and occur on trees in full vigor, upon 

limbs bearing abundant green foliage, and sometimes also 

other fruits which afterward ripen normally. 

"Often during the first year of the disease this kind of fruit 
is restricted to certain limbs, or even to single twigs, which, 
however, do not differ in appearance from other limbs of the 
tree. The following year a larger part of the tree becomes 
affected and finally the whole of it, the parts first attacked 
now showing additional symptoms, if they have not already 
done so. These symptoms are the development of the 
winter buds out of their proper season. Like the prematur- 
ing of the fruit, the date of this also varies within wide limits. 
The buds may push into shoots only a few days in advance 
of the proper time in the spring, or may begin to grow in 
early summer, soon after they are formed, and while the 
leaves on the parent stem are still bright green. This is a 
very common and characteristic symptom, and is especially 
noticeable in autumn when the normal foliage has fallen. 




Fig. 48. — Peach tree showing yellows. After Sheldon. 



94 Diseases of Economic Plants 

Usually under the influence of this disease feeble shoots also 
appear in considerable numbers on the trunk and main 
limbs. These arise from old resting buds, which are buried 
deep in the bark and wood, and remain dormant in healthy 
trees. Such shoots are sometimes unbranched, and nearly 
colorless, but the majority are green and repeatedly branched, 
making a sort of broomlike, erect, pale green, slender growth, 
filling the interior of the tree." 

A tree exhibiting these symptoms should be cut and 
burned. It is valueless, and its presence is a serious menace 
to the owner as well as to the country at large. 

Rosette. ^°^~^^^ — The peach rosette is southern in distribu- 
tion, being known chiefly in Georgia (where it was first 
noted in 1879), South Carolina, and Kansas. As to its na- 
ture, means of spread and prevention, precisely what has 
been said of yellows applies. Its distinguishing characters 
are given by Smith as follows : — 

'' Rosette clearly belongs to the same type of diseases as 
yellows, but its first stages are more striking and its prog- 
ress is much more rapid. It may first attack part of the 
tree and then the remainder, the same as the yellows, but 
it is more likely to appear at once on the whole tree, and 
generally in early spring. In trees attacked in this manner, 
all of the leaf buds grow into compact tufts or rosettes. 
These rosettes, though seldom more than two or three inches 
long, usually contain several hundred small leaves. A tree 
thus attacked always dies during the following winter or 
autumn. When part of a tree is thus attacked, that part 
dies as above described, and the remainder shows symptoms 
the next spring, to die in turn after about six months. 

"The prevailing color of the foliage is yellowish green or 
olivaceous. The older leaves at the base of the tufts are 
largest, and frequently grow to a length of several inches, 
but have inrolled margins and a peculiar stiff appearance, 
due to the fact that they are straighter than healthy leaves. 
These outer leaves turn yellow in early summer and drop 
as readily as though it were autumn, while the inner leaves 



Drupaceous Fruits 95 

of the rosette are still green and delicate. The compact 
bunching of the leaves is very conspicuous, and makes the 
trees look quite unlike those affected by yellows. Where a 
tree is attacked in all parts, it matures no fruit. In all the 
cases which have been noticed the fruit borne by affected 
trees either shrivels while green and drops off, or else ripens 
naturally. 

^'In the absence of premature, red-spotted fruit, in the 
severity of the disease from the outset, and in its rapid 
progress, it is quite unlike yellows, which is decidedly chronic, 
and the first slight symptoms of which usually occur in very 
green and thrifty trees, and are frequently overlooked the 
first season." 

The treatment is to cut and burn infected trees. No care- 
lessness should be tolerated as regards this disease or yellows. 

Little-peach. ^^^~^^^ — This seems first to have been pub- 
licly noted by Smith in an address in Michigan in 1898, in 
which state it had been of alarming character prior to 1893; 
since these years it has appeared in New York, New Jersey, 
and Canada. The most prominent symptom is small, un- 
developed fruit, one-half to one-third the usual diameter, 
ripening some 10 to 14 days later than normal fruit, and 
having ''stringy" flesh and insipid or bitter flavor. The 
somewhat drooping leaves are small, one-half normal size, 
and vary from light green to yellowish-green. An orchard 
once affected is of no further value, and should be removed 
and Inn'ned because of the danger of contagion. 

Frost Injury. — Peaches are especially susceptible. For 
discussion, see apple. 

Minor diseases 

Pustular-spot ^^"^ {Hehninthosporium carpophilufn Lev.). — 
Peaches affected with this disease are described by Selby as 
"Badly disfigured, having numerous pimply red spots with 
light brown centers." Upon yellow varieties the pustule is 
commonly lacking, there being simply a light brown center 
with a red border. As the fungus which causes this spot rests 



96 Diseases of Economic Plants 

purely upon the surface its development may be prevented 
by spraying. Selby reduced the injury from 16 per cent to 
1 per cent by three applications of Bordeaux mixture. 

Rust {Transchelia punctata (Pers.) Arth.). — A true rust 
exists upon the peach, plum, and cherry and near kin. While 
more common upon the plum, it very frequently does damage 
to the peach, in some cases being so serious as to cause almost 
complete defoliation. The alternate stage is not uncommon 
upon the hepatica in the spring. 

This malady will be recognized by the presence of small, 
round, dusty sori on the lower surface of the leaves and on 
the young shoots, while in the immediate region of these 
spore-bearing pustules, the leaf, seen from above, often 
presents a reddish or reddish yellow color. 

Stem-blight {Phoma persicce Sacc). — A fungus on the 
bark which fructifies in minute pustules sometimes causes 
twigs to die. The disease may be recognized by the dead 
bark thickly studded with small pycnidia. Burning the 
diseased branches will prevent spread of the pest. 

Frosty-mildew {Cercosporella persica Sacc). — In damp, 
shaded localities, especially on trees of dense foliage, a disease 
occurs in the form of pale-yellowish leaf spots. These show, 
on the underside, a delicate frostlike appearance, due to the 
growth of white spore-bearing hyphae. It is not usually 
serious, though widespread, and sprays recommended else- 
where suffice to hold frosty-mildew in check also. 

Cercospora shot-hole (Cercospora circumscissa Sacc). — 
This is very widespread, producing spots, or, when the 
diseased tissue falls out, oval holes, in the leaves. It also 
infects small branches. The chief injury lies in destruction 
of leaf tissue and of valuable shoots. Dormant spraying 
recommended for the curl is useful here. Phyllosticta shot- 
hole {Phyllosticta circumscissa Cke.). — Similar in appearance 
and effect to Cercospora shot-hole, it responds to like treat- 
ment. Armillaria and Clitocybe root-rots, see apple; Silver- 
leaf, see plum. 



Drupaceous Fruits 



97 



PLUM 

Black-knot ^^^ (Dihotryon morhosum (Schw.) T. & S.). — 
The black-knot receives its name from the swollen black 
distortions, 3-15 cm. long, upon the branches. In a young 
condition the galls are 
olivaceous, but as the 
season advances the}" 
become darker and 
eventually coal black. 
At the same time soft 
tissue changes to a 
hard, brittle texture. 

When the knot com- 
pletely encircles the 
twig, the supply of 
nourishment to more 
distant parts is seri- 
ously interfered with. 
If less than the whole 
of the circumference 
be involved, the dam- 
age is not so great, 
but it is even then suf- 
ficient to seriously im- 
pair the fruiting of the 
tree. Black-knot may 
either kill the tree in 
a year or two, or sim- 
ply destroy its value. 
All varieties of plums, 
and nearly all cherries, 
are subject to the dis- 
ease, which is therefore very widely distributed. It is more 
common in the East than in the West. 

It is probable that infection can occur only through injured 
bark. One step toward lessening the disease is, therefore, 




Fig. 49. — Portion of a plum tree badly 
infested with black-knot. Original. 



98 Diseases of Economic Plants 

to exercise all care not to bruise the tree. An effective meas- 
ure, however, consists in pruning out and burning all black 
knots. This course, if followed persistently and thoroughly, 
will remove all danger. Experiments show that spraying 
very materially lessens the spread of black-knot, and while it 
might not pay to spray to prevent this disease, spraying in 
an orchard for other reasons really diminishes this risk. 

Plum-pockets ^^'^' '^^'^ {Taphrina pruni (Fcl.) Tul. and T. 
communis (Sad.) Gies.). — The disease is widespread in 
Europe and the United States, and in certain localities it is 
destructive. The name ''plum-pocket," or ''plum-bladder," 
arises from the curious hollow deformity of the plum, which 
appears soon after the flowers fall. The pulp and stone of 
the fruit are replaced by a thin, soft, inflated shell, and in 
place of the seed, merely a hollow cavity exists. The affected 
fruits vary from 2-5 cm. in length, and can readily be dis- 
tinguished from the healthy fruit by their pale yellow color. 
As they age, they become coated over with a fine powder, the 
spores of the fungus. Later the pockets turn black and fall. 

The attack of the fungus is, to some extent, local in char- 
acter; thus a single tree in an orchard may bear "pockets," 
sometimes every fruit on the tree being affected, while sur- 
rounding trees are normal. A tree once affected may con- 
tinue to bear pockets in succeeding years. Treatment, in 
such cases, consists in cutting and burning the affected 
branches or trees. To some extent the disease is also due to 
yearly surface infection, which may be prevented by spraying 
as for peach curl. 

Leaf-spot ^^"^^ (Coccomyces prunophorce Higg., Cylindro- 
sporium) . — Leaf -spot or shot-hole disease, similar to that of 
plums and cherries, produces discoloration of the leaf tissue, 
the spot often bearing a red or purple border. If abundant 
several spots may coalesce as they enlarge. The tissue in- 
volved dies, turns brown, and eventually drops from the 
leaf, leaving circular or ragged holes. The disease is also 
frequent upon petioles. 

The attack is insidious, and the disease often does much 



Drupaceous Fruits 99 

damage before its presence is really known. Defoliation is 
the chief injury. This checks starch production, and thus 
impairs the tree's general vigor and productiveness, even 
weakening the tree to such an extent that it cannot with- 
stand the winter. As high as 80 per cent damage has been 
reported. The loss in Ohio was estimated as $20,000 in one 
year. Leaf-spot is especially injurious to nursery stock, as 
it may interfere with successful budding and grafting. For 
treatment, see cherry. 

Scab (Cladosporium carpophilum Thiim.). — Plum scab 
appears as spots on the fruit, similar to the scab of peaches. 
When plums begin to ripen or are just turning in color, small 
round patches, pale-greenish or grayish in color and not 
larger than the head of a pin, develop. These increase in 
size, in some cases to a centimeter in diameter. In older 
specimens the diseased spots are frequently confluent and of 
darker brown color. In very old specimens, especially where 
the fruit has undergone decomposition, the patches become 
black and uneven. 

Treatment identical with that recommended for peach 
scab will apply in this case. 

Wilt ^^'^ (Lasiodiplodia triflorce Hig.). — Restricted to 
the Japanese plum and hybrids, this injurious wilt has thus 
far been observed only in Georgia, North Carolina, and 
Alabama. Often the first symptom is a sudden wilting of the 
leaves of a single branch or of a whole tree. At the base of 
the wilted portion, the bark and cambium are dead and the 
wood brown or black. The entire tree usually dies within a 
year from the first observable wilt. The causal fungus ap- 
pears to gain entrance to the host only through wounds, and 
in the tree lives chiefly in the ducts. This disease, therefore, 
presents a case with very few parallels, i. e. of a tree killed by 
plugging of the veins by fungi. Prevention, by avoiding 
wounds, or by disinfecting them when they occur, is the only 
recourse. 

Silver-leaf {Stereum purpureum Fr.). — The leaves, though 
normal in size and form, take on an ashen gray luster, this 




Fig. 50. — Plum wilt. After Higgins, 



Drupaceous Fruits 101 

symptom showing first on single branches and extending 
year by year till the whole tree is involved. The twigs first 
infected soon die, and in the course of a few years the whole 
tree usually succumbs. The wood of diseased branches is 
browned. The sporophores of the Stereum, which appears 
to be the usual causal agent, develop only after the death 
of the tree. The disease is most common on plum and other 
drupes, but is known also on apple, pear, currant, goose- 
berry, chestnut, and ash. 

Brown-rot (Sclerotinia cinerea, Monilia). — Brown-rot is 
serious on the plum as it is with the peach and cherry. The 
loss in Ohio in one year was estimated at $25,000. 

For description and treatment, see peach. 

Minor diseases 

Blight ^^^ {Bacillus amylovorus) . — Blight of the apple 
and pear has been discussed on preceding pages. A similar 
blight is rarely known to affect the plum tree, and careful 
studies by Jones show that the diseases on plum and pear are 
identical. For treatment, see pear. For Powdery-mildew, 
see cherry. Crown-gall, Armillaria root-rot. Rust, Black- 
spot (Pseudomonas pruni), see peach. Yellows and Rosette 
are less injurious than on peach; Little-plum is similar to 
Little-peach. 



SMALL FRUITS ^s 

BLACKBERRY, DEWBERRY, RASPBERRY 

The disease of these three crops, of the genus Rubus, are 
so nearly identical that they may be treated under one 
caption. 

Anthracnose 118-120, iso {Plectodiscella veneta Burk., Glceo- 
sporimn) . — The anthracnose, on both blackberries and 
raspberries, is one of the most serious and widely distributed 
diseases of these crops. The first publication in America 
regarding it seems to have been made in 1882 by BurrilL. 
Since then numerpus papers from many sections attest its 
importance. In 1907 it was estimated to have injured one- 
third of the crop in Nebraska, one-half in Wisconsin, and 
even more in Illinois. The chief seat of attack is the cane, 
especially upon young stalks, though the disease appears 
also upon both petioles and leaves. 

The fungus often appears upon young canes before they 
are 25 cm. high, making small, purplish spots, which soon 
become grayish or dirty white in the centers. The borders of 
the spots are purplish and slightly raised. Later as the spots 
enlarge they coalesce, making irregular blotches 2 cm. or 
more long, which often encircle the cane. The stalk then 
withers and dies from lack of sap supply. Badly diseased 
canes present a bark of rough, scabby appearance due to the 
efforts of the cane to heal the wound. Canes occasionally 
crack from this disease. The chief injury is to the cambium 
layer or the sappy outer wood. The leaves on affected canes 
are dwarfed, the fruit ripens prematurely, is undersized, and 
often dries up. 

Upon the petioles of the older leaves the disease appears 
early, spreading thence along the ribs to the leaf. Owing 
to the one-sided attack upon the veins and petioles, the 

102 



Small Fruits 



103 



leaves develop unequally, 
often with inrolled edges. 
Upon the lower surface very 
small spots about 1 mm. in 
diameter are produced, from 
which the diseased tissue 
often falls. In the older 
diseased spots the spore- 
bearing acervuli are just 
visible to the naked eye. 

Occasionally, an incipient 
attack may escape observa- 
tion during the first and 
second years, and even well 
into the third year. Then, 
with prospect of a good 
yield, the berries shrivel on 
the stems and later many 
plants die. More often the 
disease remains moderately 
injurious from year to year, 
weakening the plants and 
diminishing the yield. 

In localities subject to 
this disease, it is best to 
rotate crops so as to avoid 
keeping raspberries or 
blackberries more than 
three years on the same 
soil, and to set out only 
healthy plants. When the 
disease appears, cut out and 
burn diseased parts immedi- 
ately after picking. Spray- 
ing with lime-sulfur is effective. Use three applications, 
(1) before the leaves appear, 1-20, (2) when the shoots are 
six inches high, 1-50, (3) just before blossoming. 




Fig. 51. — Anthracnose on black 
raspberry, showing typical fis- 
sures. After Burkholder. 



104 Diseases of Economic Plants 

Crown-gall (Pseudomonas tumefaciens) . — Frequently 
swellings are noticed on the stems near the roots, or even on 
the higher parts of stems, of the raspberry or blackberry 
sufficiently numerous to injure the health of the plant. 
These galls are apparently of the same nature as the crown- 
gall of the peach, almond, apple, etc. It is desirable to 
pull up and destroy diseased plants and avoid placing black- 
berries and raspberries on ground which is known to be 
infected. 

Leaf-spot {Septoria ruhi West.). — Upon the leaves of 
blackberries, raspberries, and dewberries small spots fre- 
quently appear, having a central region white or ashen in 
color, and the border brown or often of reddish tint. These 
spots are about 3 mm. in diameter. Close examination of 
the central, ashen area, especially with a hand lens, reveals 
exceedingly small, black pycnidia scattered throughout. 

While this disease is exceedingly common and of wide 
distribution, it does not often develop an epidemic and usually 
does but little injury, though its damage has been estimated 
as high as 20 per cent in Florida and Ohio. No treatment 
has yet proved of sufficient value to warrant its use. 

Orange-rust ^^^ (Gymnoconia inter stitialis (Schlecht) 
Lager.). — In the early spring the under sides of the leaves 
of blackberries and raspberries often present a livid red or 
orange color. This rust was observed as early as 1817, in 
Kamchatka, and is very widely distributed in the United 
States, Europe, and Asia, upon some nine species of Rubus, 
both cultivated and wild. It is known from Maine to 
Minnesota and Florida to California, and is in some cases 
very destructive. 

Examination of a diseased plant shows that its growth 
has been much retarded by the fungus; the leaves are curled, 
distorted, unusually small, and lacking in green color. Plants 
so affected never recover, and are useless. Preceding by 
some two or three weeks the conspicuous red rust, above 
referred to, occurs another stage of the disease that is often 
overlooked. This consists of a thick growth of small colum- 



Small Fruits 105 

nar, glandlike structures, chiefly upon the upper side of the 
leaf, and present even before the leaves unfold. These 
structures (pycnia) become more distinct as the leaves 
enlarge. 

The mycelium of the causal fungus when once established 
in the cane lives in it from year to year, spreading through- 
out the plant. Spraying is, therefore, ineffectual. In fact 
the only successful way to combat the rust is to remove 
and burn all affected plants. Diseased plants are valueless 
and are a menace to the healthy plants. Resistant varieties, 
such as the Snyder, should be used. 

Late-rust ^-'^ {Kuehneola alhida (Kiihn.) Magn.). — As 
the name implies, this rust usually appears late in the season, 
distinguishing it from orange-rust, which is prevalent in the 
spring. The spores are not so abundant as those of orange- 
rust, but occur in small, pale-yellow or whitish spots scattered 
on the under side of the leaf. This disease has not as yet 
become sufficiently prevalent to be of serious import, al- 
though its increase at any time under favorable climatic 
conditions may place it among the important plant enemies. 
It appears to be limited to blackberries, and is known both 
in Europe and the eastern United States. 

Cane-blight ^^^ (Leptosphceria coniothyrmm Sacc. Coniothy- 
rium). — First mentioned in literature in 1899 by Stewart and 
Eustace as occurring in the Hudson Valley, this disease seems 
to be widespread and destructive upon both red and black 
raspberries. Principal damage occurs to the fruiting canes, 
the foliage of which suddenly wilts and dries. New canes 
are frequently killed during the first season's growth. 

Infection usually occurs through wounds, especially 
pruning wounds or those made by insects, and progresses 
toward the root. Sometimes the disease remains upon one 
side, while in other cases it encircles the cane. 

Upon diseased canes the bark is lighter colored and dis- 
figured by smoke-colored patches of spores extruded from 
the pycnidia within. The pycnidia appear as very minute 
pustules. The wood is much discolored and eventually 



106 Diseases of Economic Plants 



Fig. 52. — Raspberry cane-blight. After Stewart and Eustace. 



Small Fruits 



107 



brittle. This cane-blight is often erroneously attributed to a 
borer or to drought, or winter injury. 

The damage is often as high as 25 
or 50 per cent of the crop, and the dis- 
ease is said to be present to some extent 
in nearly all of the raspberry planta- 
tions in New York. Cuthbert, Marl- 
boro, Ohio, Gregg, Kansas, and the 
wild red raspberry are susceptible. The 
Columbian is more resistant. 

The disease is disseminated largely 
by infected nursery stock or even by 
the soil adhering to the roots of diseased 
plants, and is conveyed from plant to 
plant by wind or rain, by pickers, or 
by workmen while pruning and layer- 
ing, also by tools used in cultivation. 
See soil diseases, p. 26. Since the fun- 
gus can live on dead fragments of canes, 
etc., upon the ground, these prove 
fruitful means of propagating the pest. 

To prevent the disease, care in the 
selection of healthy plants is necessary. 
Plants should not be set where the 
disease has prevailed in previous years. 
When the fungus has gained access to 
a plantation, all dead canes should im- 
mediately be cut out and burned and 
all fragments scrupulously removed 
from the ground. Spraying is of doubt- 
ful value. 

Spur-blight ^^^' ^^^ {Mycosphcerella 
rubina (Pk.) Jacz.). — On black and 

red raspberry canes in autumn, sharply defined, brown or 
bluish black areas from 2-10 cm. long occur on the bark, 
never on the wood. In the spring these spots bear numer- 
ous small pycnidia. 






Fig. 53. — Raspberry 
discolored by spur- 
blight. After Stew- 
art and Eustace. 



108 Diseases of Economic Plants 

This disease has been especially destructive in Colorado. 
Three applications of Bordeaux mixture, 3-2-50, with 2 
pounds of rosin-fish-oil-soap as an adhesive, applied: 
(1) when the canes were 8-12 in. high; (2) two weeks later; 
(3) two weeks later, gave excellent results in Colorado. 

Yellows. ^^^ — Affected plants are stunted, yellowish, and 
recall peach yellows. Laterals are dwarfed, leaves are small, 
curled downward at the margins, and yellow-mottled. 
Berries dry up without ripening or are insipid when mature. 
Health and disease may occur upon the same plant. The 
cane itself and roots appear normal. The disease appears to 
be limited to raspberries and has been recorded in many 
states from Massachusetts to California. 

The cause and remedy are not yet known. Diseased plants 
should be burned and resistant varieties planted. 

Gray-mold {Botrytis) , and Blue-mold {Penicillium) . — 
These molds cause decay of fruit in transit. Care to avoid 
wounds and over-ripeness, also prompt cooHng and ventila- 
tion, are necessary. 

Double-blossom * ^^^ {Fusariwm nibi Wint.). — Double- 
blossom occurs on dewberry and, to some extent, on the 
high-bush blackberry. It is most abundant on the Lucretias, 
but is also a serious pest on the Rathbone. The disease 
makes its appearance in the spring, just as the leaf buds are 
opening, although it can be detected previous to that time 
by the enlargement of the diseased buds. 

Instead of the normal shoots and leaves a witches' broom 
is produced; the entire bud being involved or only a part, 
according to the attack. When the flower buds open, they 
show a great variety of deformities: sometimes only slightly 
distorted; sometimes with increased number of stamens and 
petals and with enlarged, thickened petals and sepals. Even 
those flowers which appear most nearly perfect have dis- 
eased ovaries, and the fruits from these brooms are always 
worthless. 

Double-blossom usually appears during the second harvest 

* Prepared by M. T. Cook. 



Small Fruits 



109 



and continues to increase until the plants entirely succumb. 
Numerous late blossoms appear during the first season and 
increase in number from year to year. 

The disease is due to a fungus, and the infection of new- 
buds occurs during the blooming and fruiting season. For 




Fig. 54. — The Dewberry double-blossom showing witches-broom of 

the vine. After Cook. 



this reason it is impossible to control the disease by spraying, 
but it may be held in check by removing and burning the 
deformed buds as soon as they begin to open, and can be 
easily detected. If this is done early in the season before 
the leaves are large enough to hide the diseased parts, a 
man working alone can care for plants at the rate of 400 
per hour. 



110 Diseases of Economic Plants 

Blue-stem ^^^ {Vertidllium caulophagus (Law). — Rasp- 
berries and blackberries in the Pacific Northwest are affected 
by blue-stem, the first appearance of which was noted in 
1904. The fruit dries up before maturity, the leaves become 
discolored and wilt. Less commonly the canes turn dark, 
the first blue-black, striped discoloration of the shoot occur- 
ring near the ground. Internally in stems, and even in 
roots, reddish streaks are evident in the wood. Many 
affected canes die, others merely show the symptoms men- 
tioned above. 

BLUEBERRY AND HUCKLEBERRY 

No diseases involving special treatment are to be noted. 
Numerous parasitic fungi are recorded, among them Exo- 
basidium, Gibbera, Guignardia. 



CRANBERRY 



124-126 



To lessen storage decay, cranberries should not be picked 
when wet, nor stored with admixture of infected material 
likely to result from deep ''scooping." They should also be 
well ventilated. 

Scald, blast {Guignardia vaccinii Sh.). — The fruits are 
attacked as soon as the blossom falls, or even the blossom 
itself may be blighted. The affected berry shrivels, turns 
black, and is covered with pycnidia. From such fruits the 
disease spreads to other fruits and to the leaves. In some 
bogs as much as 50 per cent of the crop is thus de- 
stroyed. This form of disease is commonly designated 
as ''blast," while still another form of it has been termed 
"scald." 

Scald may appear upon the berries, causing small, light- 
colored, softened, watery spots. These rapidly increase in 
circumference, and even envelop the whole fruit. Sometimes 
the diseased portion shows more or less distinct brownish 
zones. In other cases the zones are lacking, and the whole 
fruit becomes very soft and translucent. Upon the leaves 



Small Fruits 



111 



irregular, reddish brown spots with pycnidia are more rarely 
produced. 

Plants, after several years of disease, die, as do cuttings 
during the first or second year. Thrifty plants are much 
more resistant than weak ones. Particular attention should, 
therefore, be given to provide such irrigation as to best favor 
the health and vigor of the plants. Sanding the fields often 
gives good results, doubtless due partly to removal of con- 
tagion by covering infective material. It is also advisable, 




Fig. 55. — Cranberry scald and blast. After Shear. 

for the same end, to rake out and burn all dead and infected 
plants in the autumn. Cuttings should be taken from such 
plants as show resistance to the disease. 

In spraying experiments by Shear, five applications of 
6-6-50 Bordeaux mixture, with 4 pounds of rosin-fish-oil- 
soap added to increase adhering power, showed 2.36 per 
cent of rotten berries, while the unsprayed plats showed 
92.6 per cent of rotten berries. The cost of application was 
$15 to $20 per acre, using 200 gallons of mixture at each 
application. 

Rot (Acanthorhynchus vacdnii Sh.). — An effect upon 
the berry very similar to that of the scald fungus appears 



112 Diseases of Economic Plants 

first as small, light-colored, soft spots, which soon destroy 
the whole berry. Later small, dark-colored blotches show 
under the skin, but no pycnidia appear. The disease is 
found in New Jersey, West Virginia, Mississippi, Wisconsin, 
and Nova Scotia. In importance it is the second cranberry 
disease. 

The treatment suggested for scald is also effective against 
this rot. 

Anthracnose (Glomerella cingulata var. vaccinii Sh.). — ■ 
This rot is less injurious in New Jersey than scald, but is 
more common in Massachusetts and New England. 

The three diseases just considered cannot well be dis- 
tinguished except by microscopic examination. In some 
cases the berry becomes soft and light-colored, but if the 
fungus develops slowly, the diseased portion is not so soft. 
To control them the water supply should be regulated so as 
to avoid great fluctuations during the growing season. 
Too little water is more to be avoided than too much. 
Vines dead from disease should be pulled and burned. 
Bordeaux mixture, at fourteen-day intervals, as suggested 
above, is recommended. 

End-rot ^^'^' ^^"^ {Fusicoccum putrefaciens Sh.). — This occurs 
in all cranberry sections of the United States, starting at 
either end of the fruit and causing softening. Bordeaux 
mixture, 4-3-50, with adhesive, applied four times, (1) before 
blossoming, (2) as soon as most of the fruit is set, (3) ten 
days later, (4) when fruit is three-fourths grown, is effective. 

Hypertrophy (Exobasidium oxy cocci Rostr.). — Hyper- 
trophy is known only in Massachusetts, where in 1906 it 
did considerable damage in some bogs. 

In this disease the buds in the leaf axils, which normally 
remain dormant, grow out into short shoots bearing swollen, 
enlarged leaves of pink or light-rose color. This character 
has given rise to the name "false blossoms." 

Wilt (Sclerotinia oxycocci Wor.). — As the plants begin to 
blossom the tips of green shoots wither. Then a thin, soft, 
white moldlike outgrowth appears upon the stem and leaves. 



Small Fruits 113 

From here the spores spread to the open blossoms and 
infect the young fruit. No further evidence of the disease 
is seen until the berry is nearly mature, when the affected 
berries are found to be full of a cottonlike growth, the 
fungous mycelium. At harvest time such berries show a 
grayish, wrinkled spot, and later the whole berry becomes 
gray, shriveled, and often spotted with dark-brown masses 
which break through the skin. Such berries carry the disease 
over winter. 

The destruction by fire of all infected fruit will lessen the 
evil in succeeding seasons. 

Gall (Sj/nchytrium vaccinii Thomas) . — The cranberry 
gall, though not widely known, has been serious in some bogs, 
and on account of its rapid spread may become of much 
import in any bog to which it gains entrance. The first 
collection of the fungus in America was by Halsted in New 
Jersey in 1886. 

It is found upon the leaves, stems, flowers, and fruit as 
small (0.8-1 mm.) red galls which occur in such profusion 
upon the affected part as to cause marked distortion. 

The disease is known to recur year after year, resulting 
in almost complete loss of the crop in infected portions of 
bogs. 

Other plants upon which this gall occurs are: Azalea 
{Rhododendron viscosum Torr.), sheep laurel {Kalmia an- 
gustifolia L.), white alder (Clethra alnifolia L.), leather leaf 
{Cassandra calyculata Don.), huckleberry {Gaylussacia res- 
inosa T. & G.), wintergreen {Gaultheria procumbens L.). 

Burning over the infested areas is recommended. 

Numerous other fungi have been recorded on the cran- 
berry, producing more or less disease. See literature cited. 



CURRANT 



130 



Cane-blight ^^^' ^^^ {Botryosphceria ribis Gr. & D., Macro- 
phoma). — This affects both currants and gooseberries and, 
reported in New York and Delaware, is probably widespread. 
A sudden wilt of the leaves on one or more canes in a bush 



114 Diseases of Economic Plants 

is the first symptom of disease. The entire bush may suc- 
cumb, but not usually during the first season. Upon splitting 
the stems a discoloration of the bark and wood near the base 
is noticed. No effective treatment is known. 

Mycosphaerella leaf-spot ^^^' ^^^ (Mycosphcerella grossularice 
(Fr.) Lind., Septoria). — The spots on the leaf are small 
(3 mm.), circular, brown-bordered, with blanched centers 




Fig, 56. — Currant leaf-spot. After Stewart and Eustace. 

which bear numerous, minute, black pycnidia. Heavy 
infection causes defoliation. Both currants and gooseberries 
are affected. Treatment is as for the following disease. 

Angular leaf-spot ^^^ {Cercospora angulata Wint.). — This 
term is applied to a peculiar spotting of the leaves of both 
currants and gooseberries. It is likely to occur wherever 
these plants are grown. The spot is of rather characteristic 
appearance, irregular or angular in outline, generally about 
3 mm. in diameter. In the center of the brown or gray, dis- 



Small Fruits 115 

colored area, hyphae may be seen. Serious defoliation often 
results. Bordeaux mixture should be used : five applications 
at ten- to fourteen-day intervals, beginning as soon as the 
leaves open. 

Anthracnose ^^^ {Pseudopeziza rihis Kleb., Gloeosporium) . — 
The leaves, fruit stalks, berries, and canes are affected. 
Usually the disease is not present to great extent, but a few- 
serious outbreaks have occurred, notably in central New 
York, in the Hudson River region, and in Oregon. It has 




Fig. 57. — Currant anthracnose. After Stewart and Eustace. 

also been noted in Ohio, Iowa, New Jersey, and is probably 
often present to a slight extent in other states. It is less 
common on gooseberries. 

In a severe outbreak the leaves first become covered with 
small, dark-brown spots, change to yellow, and soon fall. 
By the time the fruit has ripened, practically all of the 
leaves may be lost. Upon the leaf stalks, also upon the fruit, 
stems, and canes, the disease appears as little, black, sunken 
spots. On the berries the spots are circular and black, much 
resembhng fly specks. The causal fungus probably winters 
upon the canes, ready to initiate the spring infection. 



116 



Diseases of Economic Plants 



Anthracnose can readily be distinguished from the leaf 
spots mentioned above by the fact that the spots produced 
in anthracnose are very much smaller, less angular, and 
lack in every way the distinguishing characters of the other 
leaf spots. 

No conclusive evidence as to the best treatment is at hand. 
The best recommendation is probably that of the Geneva 




Fig. 58. — Anthracnose of white currants. After Clinton. 



Experiment Station: ''Spray thoroughly with Bordeaux 
mixture, commencing before the leaves appear. Make the 
second treatment as the leaves are unfolding and thereafter 
at intervals of ten to fourteen days until the fruit is two-thirds 
grown. In wet seasons make one or two applications after 
the fruit is gathered. When worms appear, add Paris green 
or green arsenoid to the Bordeaux." 

European rust {Cronartium rihicola F. v. Wal.). — Orange- 



Small Fruits 117 

colored powder appears upon the lower surface of the leaves 
of currants and gooseberries accompanied by but slight dam- 
age. The spring stage occurs upon trunks and branches of 
the white pine, and is there very destructive. For history, 
distribution, and general discussion, see pine. 

Minor diseases 

Powdery-mildew, see gooseberry ; Root-rots due to Armil- 
laria, see apple, to Fomes ribis (Schw.) Fr., see gooseberry; 
Silver-leaf, see plum ; Cluster-cup-rust, see gooseberry. 

DEWBERRY. See blackberry. 



GOOSEBERRY 



130 



Powdery-mildew ^^^ (Sphcerotheca mors-uvce (Schw.) B. & 
C). — This disease appears to be of American origin, 
whence it invaded Europe, appearing first in Russia in 1890 
and in Ireland about 1900. It is now general in Europe 
where it is much more destructive than here. The mildewed 
appearance of the leaves, stems, and fruit, all of which appear 
whitened as though dusted with flour, is characteristic. 
Close inspection shows each blotch to consist of cobwebby 
threads densely matted in the central portions of the 
spot. Later these blotches turn brown, blend irregularly 
into fewer spots, and form large diseased areas. As the 
spot ages, its threads weave together into a thick brown- 
ish felt. 

The young leaves and growing parts are robbed of nourish- 
ment, and thus their growth is checked, resulting in serious 
injury. The berries, if subjected to one-sided attack, become 
deformed and curved, owing to the retarded growth of the 
diseased side. They often crack open and decay. Diseased 
leaves turn brown. Toward the completion of the season's 
growth small, nearly microscopic, black perithecia are pro- 
duced in the centers of the diseased spots. 

The damage caused by powdery-mildew is excessive and 
presents the most serious obstacle to the successful culture 



118 



Diseases of Economic Plants 



of the gooseberry. It has quite prohibited the cultivation 
of the finer sorts of EngHsh gooseberries in America and 
is a grave menace to the culture of gooseberries in Europe. 
Its destructiveness is due not alone to injury to the 
foliage, bush, and to the fruit yield, but also to lack in 




Fig. 59. — Stages at which spraying should be given for mildew. 

After Close. 

salabihty, owing to the unsighthness of the partially diseased 
fruits. 

This powdery-mildew has been very successfully combated 
by use of potassium sulfid, 1 ounce to 2 gallons of water, or 
lime-sulfur, spraying five or six times. This treatment has 
been known to reduce the percentage of mildewed fruits 
from sixty-three on the untreated bushes to eighteen on the 
treated bushes. The proper time to spray is indicated in the 



Small Fruits 119 

accompanying figure. Treatment should be begun at the 
condition shown in the left-hand figure, and continued at 
intervals of ten days or two weeks until the requisite number 
of applications have been made. Spraying begun when the 
bushes are in the condition shown in the left figure gives 
decidedly better results than when the spraying is delayed 
until the condition shown in the other two figures. 

Cluster-cup {Pucdnia pringsheimiana Kleb., A^cidium). — 
Occasionally reddish, swollen, or thickened spots are noticed 
over the leaves and sometimes upon the fruit of currants and 
gooseberries. Close examination shows each spot to consist 
of a cluster of minute cups embedded in the tissue of the 
leaf, whence the name ''cluster-cup." With a lens each cup 
is seen to consist of a fringed rim extending above the surface 
of the leaf, and to be filled with very small, red spores. 

The winter condition is found upon quite different plants; 
namely, various common sedges (Carex) upon the leaves of 
which it constitutes a genuine rust. 

The damage is not serious, and no experiments on a large 
scale, in prevention, have been undertaken. If it should 
prove destructive, thorough eradication of the sedges in the 
neighborhood, particularly any that are rusted in autumn, 
would be deemed necessary. 

Root-rots. — Root-rots upon both the gooseberry and 
currant have been reported from various states. 

The plants die slowly. When dead and living canes are 
found in the same hill, the living canes are somewhat dwarfed. 
The fungi apparently spread through the soil, and the 
infested area enlarges year by year. 

Little can be suggested in the way of treatment. It is, 
however, best to pull up and burn affected plants, and it 
is inadvisable to place susceptible crops upon soil which is 
known to be infested. These rots have been attributed in 
part to Armillaria, see apple. 

Anthracnose and Leaf-spots are much as on the currant; 
the Blister-rust is less common than on the currant. 



120 



Diseases of Economic Plants 



« 





GRAPE 

The high acreage value of the crop, the long life of the 
individual vine, the numerous, serious diseases to which the 
vine is subject, and the fact that it was one 
of the crops first to be commercially sprayed, 
renders the grape of especial interest to the 
plant pathologist. 

Black-rot I'^^-isg (Guignardia hidwellii 
(Ell.) V. & R., Phyllostida). — This wide- 
spread and exceedingly destructive disease, 
the first record of which dates back to 1861, 
has been responsible for the abandonment 
of grape culture in many sections of the 
country. It is of general distribution 
throughout the United States, also in 
Europe and Asia. In 1906 in Michigan the 
loss from black-rot was estimated at 30 to 
40 per cent of the crop; in Ohio in 1905 at 
30 per cent of the crop worth $95,000. In 
many sections the loss is practically total 
unless measures are taken to check its 
ravages. 

In its most familiar form the disease con- 
sists of spotting and decay of the fruit. 
Black or brown spots, one or more in num- 
ber, at first infinitesimal in size, appear 
upon the berry. The spots enlarge with 
great rapidity, one spot in a few days en- 
compassing the whole berry and changing 
it into a black mass. As the rot progresses 
J^^^^^^i d the skin remains intact, and soon the berry 
F:^Kl{H».^1 begins to shrink and shrivel until it is 

eventually merely a dry, hard, wrinkled, 
mummified fruit. The rapidity with which 
this change takes place is shown in the accompanying figure. 
Many of the berries so mummified fall to the ground, others 
remain upon the vine. 





'^ 





Small Fruits 



121 



Upon the leaves the disease appears considerably earlier 
than upon the fruits. Here it produces tan-colored spots 
about 3-8 mm. in diameter, many or few according to the 
severity of the infection. In or near the centers of the older 
spots, upon the upper surface of the leaves, are seen the 
nearly microscopic pycnidia which are often arranged in 
concentric circles. 

On the young shoots the spots are somewhat more reddish 
and are often cracked longitudinally, 
but otherwise they are as upon the 
leaves. 

This rot is much more prevalent 
in warm, humid weather than in 
dry times, and a few days of muggy 
weather may so favor the growth 
of the causal fungus as to develop 
an epidemic, which may in turn be 
checked by a dry spell. Often the 
disease appears in distinct waves 
during the season, each wave cor- 
responding to a climatic condition 
favorable to infection and usually 
lagging behind such favorable con- 
dition a period of 8 to 14 days, the 
time necessary after infection for 
the disease to become conspicuous 
enough to attract the attention of 
the vineyardist. 

While the Scuppernong occa- 
sionally shows a few spots upon leaf or berry and the blossom 
is sometimes affected, this variety is practically immune. 

To prevent the inroads of black-rot, thorough, clean cul- 
ture should be practiced. All mummified fruit should be 
burned to avoid infection. Keep the ground free from 
sprouts and all other growths and permit no weeds or grass. 
Cover crops are beneficial. Plow early so as to cover all re- 
maining leaves and berries that bear the hibernating fungus. 




Fig. 61. — -Grape black- 
rot. Original. 



122 



Diseases of Economic Plants 



Use a dormant spray to clean the bark, trellis, etc. The 
utility of this first spraying may vary with climatic condi- 
tions and latitude. Use foliage sprays of 5-5-50 Bordeaux 
mixture throughout the summer. Five or six applications 
are usually necessary. The first should be made when the 
shoots are 20-30 cm. long, the others at intervals of ten to 
fourteen days. After the first two applications the spray 
must reach the clusters to be effective. Spraying each 
season is necessary; neglect one season brings large increase 
in the rot the following season. 

The following table shows the benefits of careful, thorough 
spraying. 

Result of Black-Rot Experiments in 1908 



Plat 




Net 
Weight 


Weight 


Weight 


Weight 


Firsts 
Per 
Cent 


Wine 

Per 

Cent 


Rotten 

Per 

Cent 


No. 


Treatment 


Har- 


Firsts 


Wine 


Rotten 






vested 












lb. 


lb. 


lb. 


//). 








1 


Bordeaux 
4-4-50, 6 


















applications 


8081 


7252 


742 


9,) 


89.7 


9.2 


1.1 


2 


Bordeaux 
5-5-50, 4 


















applications 


7872 


74()1 


30.5 


10 ; 


94 . 8 


3.9 


1.3 


3 


Bordeaux 
5-5-50, 6 


















applications 


9157 


872:; 


305 


125 


95 . 3 


3.3 


1.4 


4 


Sprayed ac- 
cording to 
weather con 


















ditions 


7997 


7588 


338 


71 


94.9 


4.2 


0.9 


5 


Cultivated but 


















not sprayed 


3175 


2232 


451 


492 


70.3 


14.2 


15.5 


G 


Neither culti- 
vated nor 


















sprayed .... 


333 1 


2100 


594 


571 


G5 . 1 


17.8 


17.1 



Powdery-mildew ^'''^' ^^"^ (Uncinula necator (Schw.) Burr., 
Oidium) . — This mildew was first noted in Europe about 
1845, near London, and shortly after in Belgium and France, 
and is said to have reached every grape-growing country of 
Europe before 1851. It increased in severity until 1854 when 
it began to be held in check by sulfur applications. It is 
known in all parts of the United States, but is less destructive 
here than abroad, though in certain localities in New York, 



Small Fruits 



123 



Oregon, and California, it is regarded as the most important 
grape disease. 

Powdery-mildew attacks all parts of the plant except 
the roots, showing first upon both the upper and lower 
surface of young leaves as whitish circular spots, which ap- 
pear somewhat as though dusted with flour. These spots 
enlarge, coalesce, and may cover the whole leaf. The af- 
fected leaf is retarded in growth and becomes distorted. 
Mildewed blossoms fail to set their fruit, and fruit that 




Fig. 62. — Black-rot as it shows on the leaves. 
After Anderson. 



is mildewed soon ceases growth and falls, or develops ir- 
regularly and fails to ripen. 

The mildew fungus is strictly superficial and may be 
rubbed off, leaving a discolored spot. In late stages perithecia 
may be recognized as very small black bodies, about 0.1- 
0.12 mm. in diameter, lying within the diseased areas. The 
disease develops in most destructive form in shaded, damp, 
poorly ventilated situations. Rain and fogs favor it, while 
very dry weather inhibits it. The American vines are less 
susceptible than the European varieties. 



124 



Diseases of Economic Plants 



Ventilation and removal of shading trees are beneficial. 
Close planting should be avoided in order to allow quick 
drying, trellises should run in such direction as to allow free 
access of sun. But these means are only palliative. 

To control the mildew in dry climates employ flowers of 
sulfur. The sulfur, when the temperature is above 24° C. 
(75° F.) , passes into the air, and its fumes, coming in contact 




Fig. 63. — • Black-rot spots enlarged to show the pycnidia. 
After Anderson. 



with the fungus, kill it. Below the temperature at which 
sulfur is effective the fungus will make but little progress. 
When the air, shade temperature, is from 32° to 35° C. (90° 
to 95° F.), the kilUng effect of the sulfur may be seen within 
24 hours; if above 38° C. (100° F.), one or two days are suf- 
ficient to rid the vineyard of the disease. The sulfur must 
be distributed to every part of the vine. Sulfur upon the 
ground is of no use. The vines should be dusted from one to 
seven times, according to conditions, susceptibility, climate, 
etc. The first sulfuring should be done when the blossoms 



Small Fruits 125 

begin to open; a second application should be made before 
the first sign of the mildew, and other apphcations should 
follow as need indicates. It is necessary to resulfur if from 
one to two days at 32° to 35° C. (90° to 95° F.) or four to five 
days at 29° to 32° C. (85° to 90° F.) do not intervene before 
the sulfur is removed by rain. If the disease was destructive 
the previous year, it is well to make application even earlier 
than indicated above, i. e., when the shoots are about 15- 
20 cm. long. 

After the grapes commence to ripen they are comparatively 
safe from mildew, but for the future good of the vine the 
leaves should be protected by further sulfuring if need be. 
Young vines should similarly be protected. To properly 
apply, use good dusting machines which give an even flow 
of sulfur and are easy of operation. 

In climates where sulfur cannot be used to advantage 
reliance must be placed upon Bordeaux mixture or lime- 
sulfur applied as for the black-rot. 

Downy-mildew ^^^' ^^^' ^^^ {Plasmopara viticola (B. & C.) 
Berl. & de Toni). — Downy-mildew produces a more or 
less distinctly visible downy or velvety growth upon the 
affected surface, caused by myriads of spore-bearing stalks 
that rise from the diseased surface. If these stalks are 
close together, the appearance is thoroughly characteristic 
and the diagnosis clear. As the spores mature the spots 
assume a gray or frosted appearance. 

The European grapes are more susceptible to this mildew 
than the American varieties. All the green parts of the plant 
are affected. Upon the lower side of the leaf the disease 
may be recognized by the description given above. The 
upper surface of the leaf over a diseased spot becomes pale, 
yellowish, and finally turns brown and dies. The area so 
affected is definitely bordered and does not necessarily 
cause the death of the whole leaf, though it may do so. 

Upon shoots the same characteristic appearance is noted 
as upon the lower surfaces of the leaves. Sometimes the 
death of the affected twig or even of the whole vine results. 



126 



Diseases of Economic Plants 




Fig. 64. — Downy-mildew as seen from the lower surface of the leaf. After Heald. 



Small Fruits 



127 



Immature berries which are affected cease growing and de- 
velop the same coating noted upon the leaves, giving rise to 
the name "gray-rot." If the berries are more mature when 
attacked, they turn brown, thus calling forth the name 
"brown-rot." The berry in dying shrivels and becomes 




Fig. 65. — Young Niagara clusters attacked l)y downy-uiildew. 

After Lodeman. 

wrinkled, but does not become hard and dry, as in the case 
of the black-rot. The disease is usually more troublesome 
in the early part of the season than in autumn. Effective 
management requires early Bordeaux spraying, just before 
the blossoms open, and often it will be found advantageous 
to protect the leaves by two to five additional sprayings at 
intervals of about two weeks. This disease was noted in 



128 



Diseases of Economic Plants 



America as early as 1834, and was carried to Europe about 
1878. It is now general both in Europe and the United 
States. 

Anthracnose ^^^' ^^^ {Gloeosporium ampelophagumSsiCC.). — 
This anthracnose, probably introduced into America from 
Europe prior to 1880, is now widely distributed throughout 




Fig, 66, — Anthracnose on the fruit. After Paddock. 

grape-growing sections and is the fourth disease in impor- 
tance. While not usually so destructive as black-rot or 
brown-rot, it sometimes increases to such an extent as to do 
great damage, even causing in some instances the loss of all 
the berries upon a vine as well as much injury to the canes. 
During damp, warm weather it develops rapidly, affecting 
some varieties more than others. The Champion and 
Moore's Diamond may be mentioned as especially sus- 
ceptible, while the Concord is resistant. 



Small Fruits 129 

Upon the canes the anthracnose is first seen as small, dark 
brown or black spots, which soon become sunken in the 
centers. The spots usually enlarge rapidly lengthwise of the 
stem, though they may sometimes girdle it. Girdling is 
particularly common upon stem clusters, where it is always 
fatal. The centers of the older spots are ashen in color, the 
edges dark, and the cankerlike spot extends from the bark 
deep into the wood, rendering the shoot weak and brittle. 

Upon the fruit, spots 3-5 mm. in diameter are produced 
similar to those upon the canes, except that the center does 
not always become ashen. Here, too, a band of red often 
surrounds the diseased part. The parts of the berry adja- 
cent to the diseased spot remain green and develop normally, 
which, associated with the red border, results in the peculiar 
appearance which has led this disease to bear the name 
"bird's-eye disease." 

If the berry is attacked while young, it may either out- 
grow the disease or succumb to it. Several spots upon one 
berry destroy its value, and spots upon one side may cause 
distortion, cracking, and exposure of the seeds. 

Upon the leaves the dead spots are usually bordered by a 
fine black line, and as the leaf enlarges the dead tissue of the 
spot may rupture irregularly. 

Badly anthracnosed canes must be cut out and burned, 
and a dormant spray applied, followed by protective sprays 
as for black-rot. 

Necrosis, Dead-arm ^^^' '^^^ {Cryptosporella viticola (Red.) 
Sh., Fusicoccum) . — This disease has been noted in New 
York, Ohio, Georgia, and Indiana. It is said to cause loss of 
from 1 to 5 per cent annually in New York. The Concord, 
Niagara, Moore's Early, Agawams, Pocklingtons, Wordens, 
Lindleys, Catawbas, Isabellas, and Scuppernong are sus- 
ceptible. 

Necrosis may be recognized in the field by the following 
characters: A trimmed and tied vine that has failed to 
put out shoots; one that has sent forth shoots, the latter 
dying after a few weeks; vines on which all or part of the 



130 



Diseases of Economic Plants 



shoots and leaves exhibit a dwarfing, with leaves small and 
often crimped about the margin ; leaves of nearly normal size 
but blanched; apparently healthy vines with leaves and fruit 
shriveling and dying in the summer; fleshy or corky longi- 
tudinal excrescences on the stem, which in the autumn dry 
down and become reddish brown and the following spring 
slough off; the presence of minute black pustules on a dead 

spur, bark, or wood under 
the bark; small reddish brown 
spots 3-4 mm. long on the 
green shoots. 

The disease is conveyed to 
new tissue by spores from 
the pycnidia, also probably 
by pruning tools. It may 
also enter the older parts 
through wounds. Cuttings 
bearing the fungus probably 
spread the disease. 

Spraying shoots with Bor- 
deaux mixture when from 
73/^-15 cm. long will reduce 
infection. Diseased vines should be pulled and burned, or 
if the root crown be still sound, they may be cut back to 
near the ground, when the renewal will be healthy. In the 
spring and summer it is well to mark sick vines for future 
eradication. Cut off the diseased parts, using tools not 
used in ordinary pruning. 

Root-rot ^^^ (various fungi). — This rot attacks a few 
roots at first, but eventually reaches all, and results in death 
of the vine. It is very destructive in Europe and has been 
noted in several places in the United States. 

The top growths of affected vines show symptoms first; 
then follows one division after another until a large vine 
is reduced to the size of a bushel basket, though numer- 
ous lateral canes may arise, especially near the base of the 
plant. The leaf color usually remains normal v/ith no dead 



-& 


.^'it 




M 


tl^-si 


fi 




i 




1 


aH^Hb ^^JKj^h^P 



Fig. 67. — Necrosis of the vine. 
After Reddick. 



Small Fruits 



131 



tissue, though the leaves sometimes turn 
yellow, and many of them are reduced in 
size. After the vine dies the leaves still re- 
main attached to the canes. The best treat- 
ment is to remove and burn the affected 
stock, thoroughly stir, air, and dry the adja- 
cent soil. For further discussion of root-rot, 
see p. 370. 

Several diseases, the causes of which are 
not known, do serious injury to the grape. 
They may be briefly described as follows: 
California vine-disease. ^^*^ Since 1884 
many vineyards in California have been 
destroyed by this disease. In the first sea- 
son small, yellow spots appear between the 
veins. These enlarge and unite to form 
stripes, leaving only a narrow band of green 
tissue along the veins. Leaves fall prema- 
turely and the canes turn black and die. 
The following season there is reduced growth 
of canes. By the third or fourth season the 
vines usually die. Cuttings should not be 
made from diseased vines. An unnamed 
disease of somewhat similar character has 
been described in New York.^^^ Brunissure. 
Irregular brown spots appear on the upper 
surfaces of the leaves and the epidermis 
falls away, exposing the underlying tissue. 
Later the browning extends through to the 
lower leaf surface. Black zones often ap- 
pear in the wood. Shelling consists in the 
grapes falling from their stems before ma- 
turity. Diseased berries are matted, thick- 
skinned, and show a brown zone beneath 
the skin. Though the cause of shelling is 
unknown, it is more common on weak 
vines. Good cultural conditions lessen it. 




Fig. 68. — Grape 
necrosis as it 
appears on the 
canes. After 
Reddick. 



132 Diseases of Economic Plants 

Blue-mold rot ^^^ {Penicillium) . — Grapes should be handled 
to avoid wounds, carefully packed, and shipped or stored at 
as nearly 0° C. (32° F.) as possible to prevent large loss due 
to blue-mold. 

Minor diseases 

Crown-galP'^'' (see apple) is common on the grape, with 
a wide difference in susceptibility between varieties; Bitter- 
rot comes late in the season on the fruit when nearly ripe, see 
apple; White-rot (Charrina), Scab (Cladosporium viticolum 
Ces.), Gray-rot (Sclerotinia fuckeliana (De Bary) FcL), and 
Cercospora leaf-spot are usually of but little injury. 

HUCKLEBERRY. See blueberry. 

RASPBERRY. See blackberry. 

STRAWBERRY 

Leaf-spot ^^^' ^^^ {MycosphcereUa fragarioe (Tul.) Lin., 
Ramularia), — The most conspicuous disease of the straw- 
berry, one nearly always present to some extent on both wild 
and cultivated varieties in Europe and America, is recognized 
by the presence of small, 4-6 mm., purple or red-bordered 
spots upon the leaves, the older spots bearing white or ashen 
centers. Late in the development of the spots the hyphae of 
the causal fungus are barely visible with a good hand lens. 
The spots, when numerous, may coalesce, forming large, 
irregular blotches. The disease is also very injurious in its 
attacks upon the fruit stems, resulting in diminution of food 
supply to the fruit and its improper development. 

It attacks all varieties, precluding the use of especially 
susceptible varieties in some localities, often killing the 
plants, and in any event lessening their vigor and produc- 
tiveness. In some localities entire plantings have been de- 
stroyed. One grower reports a loss of $1500 on a six-acre 
field in one season. 



Small Fruits 



133 



Moisture and heat favor the development of the fungus, 
while moisture upon the leaves is essential to infection. 
Weather favorable to infection followed by hot, dry days 
may be attended by great injury. Heavy, wet, undrained 
soil also conduces to disease. 




Fig. 69. — Strawberry leaf-spot. After Freeman. 



Frequent change of beds; also cutting, gathering, and 
burning or burying of tops in place after harvest, and the use 
of Bordeaux mixture after the removal of the diseased leaves 
will lessen the infection of the next year. 

Hume in Florida found that by means of three early spray- 
ings of 4-4-40 Bordeaux mixture, the disease was so checked 
that ''it was a difficult matter to find a leaf at all diseased in 
the whole patch." Later, when the disease began to make 
headway again, another spraying controlled it. 



134 Diseases of Economic Plants 

Powdery-mildew {Sphceroiheca humuli (DC.) Burr.). — 
This mildew may be recognized by the characters usually 
pertaining to the powdery-mildews. (See grape.) 

Upon the strawberry it induces curled, in-rolled leaves, 
and the white mycelium is found upon their lower surfaces. 

The disease is not usually troublesome. 

Botrytis-rot ^^'^ {Botrytis sp.). — This rot, though prevalent 
in the field, occasions serious loss only on berries which are 
shipped over long hauls. The rotten spot is dry, tan-colored, 
and finally covered with downy spore clusters. Careful 
sorting to avoid shipping of infected berries is necessary. 
Infected fruit that is sorted out should be buried with lime. 

Leak ^^^ (Rhizopus nigricans Ehr.). — Berries often decay 
in shipment, the juices leaking out from the bottoms of the 
boxes. The berries sink to a feltlike layer covered by mold 
and its black sporangia. This rot causes millions of dollars 
loss annually. Only sound berries should be offered for ship- 
ment. 

Minor diseases 

Leaf -blight ^'^^ due to Aposphseria; Leaf-spot due to 
Ascochyta; Fruit rots due to Sphaeronemella,^^^ Patelhna,^''^ 
and occasionally to the black-rot fungus, Physalospora,^^'' 
do some injury. 



TROPICAL FRUITS 

AVOCADO 

Anthracnose (Colletotrichum gloeosporioides Peiiz.). — At- 
tack upon the leaves eventually causes defoliation. Early 
infection of the fruit results in its complete loss. If the 
fruit is not attacked until late, it may remain upon the 
tree, but becomes brown spotted and finally cracked. On 
both leaves and fruit anthracnose can be controlled by the 
use of Bordeaux mixture. A rot of the tree trunk is caused 
by Pythiacystis, and a leaf-spot by Mycosphaerella. ^^^ 

BANANA AND PLANTAINS 

Wilts ^'^^' '^"^^ bacterial and fusarial, are of wide distribution. 
One of these is said to have caused the abandonment of 
nearly 20,000 acres of bananas in Panama. 

Anthracnose (Gloeosporium musarum C. & M.) frequently 
develops on ripe fruit in the market, but really does but little 
injury. 

CACAO ^^1 

This important crop is subject to numerous destructive 
diseases , the most serious of which are : Canker and Pod 
black-rot, due to Phytophthora; Die-back due to Diplodia; 
Pmk-disease (Cortidum) which kills even large branches, 
and Witches-broom {Colletotrichum). Other cankers are 
caused by Nectrias. 

CITRUS FRUITS ^^° 

Brown-rot ^'^^ (Pythiacystis dtrophthora S. & S.). — This 
disease has caused a very considerable loss, 30 per cent in 
some cases, in California but the real origin of the trouble 

135 



136 



Diseases of Economic Plants 



was not known until 1906 or 1907. It chiefly affects the 
fruit after it has been packed and shipped to market, al- 
though the infection takes place in the orchard or packing- 
house, where the disease is largely disseminated by the fruit 
washers. 

The rot has a peculiar characteristic rancid, penetrating 
odor, and its presence is further indicated by the prevalence 




Fig. 70. — Brown-rot of lemons, showing white growth of the 
fungus. After R. E. Smith. 

of small flies in boxes where there is diseased fruit. One 
affected fruit in a box communicates disease to the whole. 

Brown-rot is found in nearly pure condition on the fruit in 
the orchard, especially on fallen fruit or on fruit hanging low 
on the tree. It is most prevalent in wet weather or on low 
ground after irrigation. The fungus is visible to the eye in 
the packing-house, as a mass of white filaments. It is spread 
by contact alone. 

Orchard infection can be controlled by the use of a heavy 
mulch under the trees, either straw or a heavy cover crop. 



Tropical Fruits 137 

In the packing-house the use of disinfectants in the washer 
prevents trouble; one pint of formahn to 1250 gallons of 
water, or 1 pound of copper sulfate to 625 gallons of water. 

Cottony-rot ^''- (Sderotinia lihertiana) . — The fungus on 
lemons is identical with that of lettuce drop, and its mycelium 
and sclerotia appear as described under that disease. The 
decay spreads rapidly from fruit to fruit in storage, and the 
loss is considerable. Twig, blossom, or seedling infection of 
oranges or lemons, accompanied b}^ gummosis, also occurs. 
Disinfection of the fruit with 1/50 per cent solution of copper 
sulfate is employed. 

Canker * ^^9^^^- {Psevdomonas citri Hasse) . — Citrus canker 
is one of the most destructive diseases introduced into the 
United States in recent years. Its nature was first pointed 
out by Hasse in 1915. Before that time it was thought to be 
caused by fungi and was confused with citrus scab. The 
origin of the disease is obscure. It was first described from 
the southernmost island of Japan in 1899 on navel oranges, 
where it was undoubtedly introduced from South China. 
About 1910-11 citrus canker was introduced directly from 
Japan into Texas on the trifoliate orange and on nursery 
stock. In a short time it was carried into other Gulf states 
on infected plants, imported directly from Japan and in- 
directly from Texas, so that by 1914 it had assumed the 
aspects of an epidemic in certain parts of Florida, Alabama, 
Mississippi, Louisiana, and Texas. About the same time 
outbreaks were reported from two areas in the Transvaal, 
South Africa, the Philippine Islands, and later from North 
Australia; originating in importations from Japan. 

Citrus canker, while primarily a leaf spot, may attack parts 
of the tree above ground. On the leaves, the young spots 
usually appear on the under side as small, yellow, translucent, 
oily pimples. Later they rupture to form brown, raised, 
corky spots with an oily outline, and sometimes a wide, 
yellow margin. The spots break through to the upper side 
of the leaf. The young spots on the twigs and branches are 
* Prepared by G. L. Peltier. 



138 Diseases of Economic Plants 

similar to those on leaves, but usually they become more 
corky and have a tendency to girdle the twig or branch. On 
the fruit the old cankers are superficial and very corky. 

Infection, in the absence of wounds, takes place through 
the stomata. The period of incubation varies from two or 
three days to several weeks. The factors favoring infection 
are a high temperature, a relatively high humidity, and a 
rapidly growing plant. The organism survives the colder 
months in the spots on the twigs and branches. Under cer- 
tain conditions the organisms may lie dormant in the bark 
for several months. 

Pseudomonas citri has a wide range of Rutaceous hosts, 
including all the plants and hybrids of the genus Citrus, 
although some show considerable resistance. The order of 
susceptibility of the more important commercial citrus 
fruits and stocks is provisionally as follows: grape fruits, 
trifoliate oranges, lemons, sour oranges, sweet oranges, limes, 
citrons, mandarin oranges, and kumquats. Several new 
introductions of citrus fruits and hybrids, originated by 
Swingle, show considerable resistance and promise to super- 
sede the more susceptible fruits in some instances. 

Infected nursery stock was wholly responsible for the 
spread of citrus canker from state to state. However, owing 
to rigid quarantine measures, further danger from this source 
appears to be eliminated. The combination of wind and 
rain is most important in the spread of canker from tree 
to tree; other agents are dust, insects, birds, man, and other 
animals. 

Owing to the rapidity with which citrus canker spreads and 
its menace to the citrus industry of the Gulf states, drastic 
measures for its control were adopted in 1914-15 in all the 
Gulf states. These consisted in burning all infected trees 
as soon as they were found. 

The number of infected citrus trees found in Florida in 
August, 1914, was 1313. During 1918 only 15 were found, 
and in 1919 only 4 infected trees. Few possible centers of 
infection remain in the United States. 




Fig. 71. — Citrus canker. After Webber. 



140 



Diseases of Economic Plants 



Scaly-bark ^^^ {Cladosporium herharum Lk. var. dtricolum 
Faw.). — Small, circular, or oval, rusty-colored spots with 
well-defined margins, on both bark and fruit, characterize 
this disease. The bark cracks and forms scales. The spots 
are at first scattered, but in time coalesce and form large areas 
upon the branches and trunk, giving it a scaly appearance. 




Fig. 72. — Scaly-bark injury to fruit. After Stevens. 



Similar injury also occurs on the fruit (Fig. 72). Sweet 
oranges are most affected, the fruit ripening prematurely. 

Top working is recommended, also heading back and 
painting the trunk and the stumps of the branches with 
carbolineum and water equal parts. 

Gummosis. — Several diseases recognized by the exuda- 
tion of gum from the trunks and branches of the trees are 



Tropical Fruits 141 

called "gum diseases." Their causes are not definitely 
known; by some they are attributed to mechanical injury 
alone; by others to poor cultivation or water injury in ir- 
rigation; by others to the presence of soil around the trunk; 
by still others to fungi. 

Blue-mold, rot ^^^ {Penicillium italicum Wehm., and Penicil- 
lium digitatum (Fr.) Sacc). — This decay of citrus fruits in 
transit from California causes a loss estimated in 1908 as 
being between $500,000 to $1,500,000 annually. Careful in- 
vestigations of Powell and his assistants have shown that the 




Fig. 73. — Two forms of blue-mold: at left, Penicillium italicum; at 
right, P. digitatum. After R. E. Smith. 

chief trouble results from wounds on fruit in handling, which 
thus provide an entering point for the fungus. Without me- 
chanical injury no decay from blue-mold can occur. Hence 
the method of control is painstaking care in handling the 
fruit to prevent bruising or puncturing the skin. 

Black-rot ^^^ (Alternaria citri Pierce). — This disease was 
described and its cause given by Pierce in 1902. It attacks 
only the navel orange, causing from 2 to 5 per cent loss 
of the whole crop. It is easily recognized by the prema- 
ture ripening which it induces, and by the deep red color 
and extra large size of the fruit. The diseased fruits are 
very conspicuous on the trees before the main crop has col- 



142 



Diseases of Economic Plants 



ored. A considerable portion of the ''June-drop" is caused 
by this disease. 

The spores of the fungus gain entrance through shght 
imperfections of the skin at the navel end, producing de- 
cayed areas under the skin. 

All diseased fruit should be collected and burned or buried 
deeply. 

Scab (Cladosporium citri Mass.). — Scab has been known 




Fig. 74. — Scab of the sour orange. After Hume. 

for twenty years, and occurs on the sour citrus fruits, such 
as the pomelo, kumquat, and sour orange. 

The disease attacks the young leaves, twigs, and fruit, 
and causes them to produce conspicuous, warty, corky 
growths, that give a rough, uninviting appearance. Often 
the leaves are twisted and drawn out of shape. The warts 



Tropical Fruits 



143 



are at first yellowish, b\it as the disease advances they become 
almost black, and finally crack open. 

Ammoniacal copper carbonate or Bordeaux mixture will 
prevent scab. 

Anthracnose, wither-tip {Colletotrichum gloeosporioides 
Penz.). — In this disease the leaf spots are circular in out- 
line, yellowish in color, and bear the small dark filaments and 
spores of the causal fungus. 
Terminal twigs shed their 
leaves and die. 

The disease also occurs 
upon the fruit of various 
citrus trees. Rolfs noted 
its attack upon the lemon, 
where it caused the fruit 
to fall prematurely, and 
Hume reports that it may 
occur upon the pomelo 
either before or after 
the fruit is picked. The 
brownish spots enlarge with 
age and become dirty 
black in color. The fun- 
gus invades the interior of 
the fruit as well as the rind. 

In all cases the diseased parts should be cut out, care being 
taken to cut far enough back to remove all injured" parts; 
also affected fruits should be removed and destroyed. Spray- 
ing with Bordeaux mixture controls the disease upon the 
fruit. 

Root-rot {PMjtophthora terrestria Sherb.). — The first symp- 
toms are abundant exudations of gum upon the trunk of the 
tree; at the same time the bark develops brownish patches, 
which are thrown off, followed by other patches. The tree 
appears to lack nutrition, the leaves becoming yellow, scanty, 
and small. Though the trees bear considerable fruit, the 
amount of damage in Florida was estunated in 1896 to be 




Fig. 75. — Orange leaves showing 
spots caused by anthracnose. Af- 
ter Hume, 



144 Diseases of Economic Plants 

$100,000 annually. Resistant stock should be used; diseased 
parts should be excised, and antiseptics applied. 

Die-back is characterized by gum pockets, stained terminal 
branches, ammoniated fruits, bark excrescences, and multiple 
buds. The disease is important but the cause is unknown. 

Melanose (Phornopsis citri Faw.) is a disease of foliage, 
young twigs, and fruits, in which small, dark, elongated spots 
are produced. Weak Bordeaux mixture should be used. 

Blight, with wilting of foliage and death of twigs and 
branches, is of unknown cause. In many ways it resembles 
peach yellows. 

Minor diseases 

Citrus-knot {Sphceropsis tumefadens Hed.), troublesome 
in Jamaica, and once found in Florida; various leaf-spots; 
Sooty-mold ^^^' ^^^ consisting of a black, superficial fungus 
(Capnodium) ; Algal leaf-spot produced by Cephaleuros 
virescens; Crustose lichens; Dodder and Mistletoe, occa- 
sionally attacking citrus fruit trees; Sour-rot of lemons 
{Oidium citri-aurantii) , also called slimy-rot and watery- 
rot occurring during storage; Crown-rot (Sclerotium rolfsii); 
Wood-rot due to several large fungi ; Die-back and stem-end- 
rot (Diplodia), and Pink-disease (Cortidum) are of minor 
importance. 

COCOANUT 

Bud-rot ^^"^ {Bacillus coli (Esch.) Mig.) is the most seri- 
ous disease of this palm. It is of wide and growing dis- 
tribution in the American and Eastern tropics. An annual 
loss of £4500 is reported from one plantation in Jamaica. 
A soft rot occurs in the terminal bud, the growing point, re- 
sulting in the death of the tree. Badly diseased trees and all 
infected refuse should be burned. 

COFFEE 

Rust (Hemileia vastatrix B. & B.). — This most destruc- 
tive coffee disease, believed to have spread to coffee from 



Tropical Fruits 145 

some weedy Rubiaceous host, is widely present through the 
Old World. It was introduced into Porto Rico some years 
ago, but prompt recognition and effective action by the 
Porto Rican Experiment Station exterminated it in the 
Western Hemisphere. 

Viruela {Stilbella flavida (Cke.) Kohl.). — This is the most 
serious coffee disease of the Western Hemisphere, causing 
circular, decayed, tan-colored leaf-spots, leading to rapid 
defoliation. 

Leaf-spot (Cercospora coffeicola B. & C). — Numerous, 
circular, brown spots occur, causing leaf-fall. The fungus 
grows also on the berries. Other leaf-spot fungi are Col- 
letotrichum, Gloeosporium, Anthostomella, Hendersonia and 
Rhabdospora. 

Leaf -rot ^'' {Corticium koleroga (Cke.) v. Hohn.). — The 
causal fungus grows on the stems, leaves, and fruit, spread- 
ing as a smooth, tissue-like, whitish film. Rot of the affected 
parts follows. 

Stem-disease (Necator decretus Mass.). — Minute orange 
spots are produced. 

Root-rot due to various fungi is destructive. 



FIG 



166 



Fruit-rot {Colletotrichum carica S. & H.). — This disease, 
first described in 1909, produces sunken, rotten, more or less 
circular fruit spots, nearly always covered with a white 
mass of fungous mycelium. As the spots grow older they 
bear numerous pustules of the salmon-pink color characteris- 
tic of the spores. 

The amount of damage caused is very great by reason 
of premature falling of the fruit, at times destroying the 
whole of the crop. 

Infected fruit should be gathered and destroyed and 
the bushes should be given a dormant spray and two or more 
applications of Bordeaux mixture when in foliage. 

Rust {Physopella fid (Cast.) Arth.). — This rust does 



146 



Diseases of Economic Plants 




Fig. 76. — Fig in well-advanced 
stage of fruit-rot. Original. 



considerable damage, causing 
premature falling of leaves. The 
rust appears as brown spots 
upon the leaf. 

Leaf-blight {Cercospora bol- 
leana (Thtim.) Speg.). — This 
blight has been noted in the 
United States, though l)ut slight 
attention has been given it. It 
causes injury similar to that of 
rust. 

Other diseases of the fig are: 
a root-knot due to nematodes; 



a Rhizoctonia leaf-blight; 
Southern-blight (Sderotium rolfsii) ; Cankers due to Mac- 
rophoma, Libertella, and Tubercularia; Limb-blight due to 
Corticium; Root-rot (Ozonium) and Yellow-rust (Fusarium), 
Black-smut ^^^ (Sterigmatocystis) may affect as high as 15 per 
cent of the fruits in some instances. 



GUAVA 

Ripe-rot {Glomerella psidii (G. Del.) Sheldon). — This 
disease was 
described 
from green- 
house mate- 
rial collected 
at Washing- 
ton, D. C, 
and after- 
ward it was 
reported 
from Florida 
and Cali- 
fornia. The 
affected 
fruit shows 
circular, 




Fig. 77. — Guava affected with ripe- rot. After Rumsey. 



Tropical Fruits 



147 



brown decayed areas. In older stages, masses of salmon- 
colored spores are visible over the decayed areas. The 
entire fruit at length becomes rotten, wrinkled, and shrunken. 
Algal leaf-spot (Cephaleuros virescens) is common. 

LOQUAT 

Scab {Fusicladium dendriticum (Wallr.) FcL, var. erioho- 
tryce Scalia.). — In the western part of California scab is 
reported as serious upon both fruit and leaves. 



MANGO 

Anthracnose ^^^' ^""^ (Colletotrichuingloeosporioides Penz.). — 
This rot of the fruit, flowers, and leaves resembles bitter-rot of 
the apple, and causes much loss in 
the Caribbean region, in Hawaii, 
and the Gulf states. 

OLIVE 

Knot (Pseudomonas savastanoi 
EFS.). — Tubercles or galls upon 
the leaves and branches, and even 
upon the trunk of the tree, are the 
first signs of attack. Upon the 
leaves, the knots are always small, 
particularly if they are numerous. 
Upon the small twigs the knots 
attain the size of a garden pea, 
while upon the trunk they become 
2-3 cm. or more in diameter and 
finally destroy the tree. The dis- 
ease was noticed in California in 
1893 and appears to be confined 
to a very small range. Excision 
should be practiced. 

Leaf-spot {Ctjdoconium oleagi- 
num Cast). — According to Bioletti 




Fig. 78. 



R 



Olive knot. 
E. Smith. 



After 



148 Diseases of Economic Plants 

this disease is prevalent in certain regions of California, 
occasionally causing the leaves to turn yellow and injur- 
ing the appearance of the fruit. Usually it does but 
little harm. Spots 2-4 mm. in diameter occur upon the 
leaves. They are composed of concentric rings of different 
colors, giving them somewhat the appearance of the spots on 
peacock tail feathers. The spots on the fruit are smaller and 
more decidedly brown in color. 

The use of Bordeaux mixture checks the trouble. 

Sooty-mold occurs much as on citrus fruits and Root-rot 
{Armillaria niellea) as on other orchard trees, p. 51. 

PINEAPPLE 

Black-heart (Thiehtviopsis paradoxa (d. Seyn.) v. Hohn). — 
This rot of fruit may be found in abundance in any market 
and causes the loss of many carloads of fruit. It usually 
begins at the stem-end and progresses through the center of 
the fruit as a soft rot, in later stages turning black, due to the 
formation of many spores. Other fruit rots are due to 
Diplodia, Trichosphseria, Penicillium. Other pineapple dis- 
eases are: Rot of young plants due to soil fungi, Wilt and 
Chlorosis. 

PLANTAINS. See banana. 

VANILLA 

Numerous diseases are recorded on this orchid. The most 
destructive is caused by Calospora vanillce Mass., which 
grows on stems and leaves, and eventually kills the entire 
plant. Other parasites are Vermicularia, Colletotrichum, 
Glceosporium, Uredo, Uromyces and Nectria. 



VEGETABLE AND FIELD CROPS 



172, 177 



These crops cover a wide range in cost of production ; some 
being grown in glass houses with artificial heat, others under 
canvas in cold frames, still others under ordinary field condi- 
tions. With crops of high value, correspondingly expensive 
methods of disease control are warranted, while with the 
field crops, resort must be to spraying or to less expensive, 
general methods of sanitation and field practice. 

The crops following are arranged alphabetically by their 
common names, except that several crops of a botanical 
family when generally affected by the same diseases, for 
convenience of discussion, are grouped together. 

ASPARAGUS 

Rust ^'^^"^'^ {Puccinia asj)aragi DC). — Asparagus rust, 
though observed in Europe as early as 1805, was not noted 
in epidemic form in the United States until 1896, when it 
was recorded by Halsted as occurring in several New Eng- 
land States. In 1897, though it had passed to South Carolina 
and to some extent westward, the interior and western part 
of the United States seemed still free from it. In 1898 it was 
first found in Michigan; in 1899 in Illinois, Ohio, and Kansas; 
in 1900 in Dakota, Nebraska, and Texas, completing its 
westward march into California in 1900 or 1901. Now it is 
found in every state where asparagus is grown. 

Rust usually first attracts attention by its effect upon the 
green tops which redden under the disease, this symptom 
appearing at any time after blossoming or coming to leaf. 
Diseased areas in the field enlarge rapidly, and soon the 
affected leaves yellow and fall, leaving the bare, dead stalks. 
Close examination in the field shows that the twigs and 
leaves bear many small skin blisters (sori) under which is a 

149 



150 



Diseases of Economic Plants 



mass of powder nearly the color of iron rust. In early stages 
of attack these blisters are few and scattered, but they 
rapidly increase in number. When young, the skin covering 
the sori is unbroken ; later it ruptures, setting loose the rusty, 
powdery mass of spores beneath. This, the summer stage, is 

chiefly responsible for the 
hibernation of rust in the 
East. Later in the season 
the sori become black in- 
stead of rusty-colored, thus 
constituting the winter 
stage of the rust. 

In the spring still an- 
other stage, the spring 
stage, may occasionally be 
seen, though it is rare east 
of the Rocky Mountains. 
This consists of small, 
oval, pale spots upon the 
branches or leaves. In the 
centers of these spots small 
round pustules develop in 
concentric lines. Soon 
each pustule opens, con- 
stituting a very minute cup 
which is sunken into the 
leaf. From these cups 
issues a powder quite sim- 
ilar to that from the sori 
of the summer stage, 
though more orange in 
color. All three stages of rust — spring, summer, and win- 
ter — may occur simultaneously upon the same plant. 

The disease spreads rapidly throughout the field during the 
spring and summer stages. The winter stage is the typical 
hibernating condition in which the causal fungus may rest un- 
til the following spring before it can induce further infection. 




Fig. 79. — Sori ot the asparagus rust 
upon the stems, enlarged. Original. 



Vegetable and Field Crops 151 

During the first two stages spores in enormous quanti- 
ties are liberated by the least movement of the plants, by 
animals or wind, and the spores, carried to their new prey, 
produce infection if conditions of moisture are present. 

While the salable part of the plant is not attacked, the 
green part is largely decreased, so that the amount of nutri- 
ment that can be stored away in the underground parts is 
lessened. This results in diminished vigor and productive- 
ness of such roots the following season. The loss may range 
from 15 to 35 per cent of the crop the year after the first 
attack, while in three years the more susceptible varieties 
may be so nearly destroyed as to necessitate the abandon- 
ment of the beds. 

Rust is most injurious in light, dry soil; irrigation is, there- 
fore, beneficial. Dew has been found to favor rust; there- 
fore shaded, dewy localities should be shunned, as should also 
rows running at right angles to the prevailing winds. Clean 
culture methods, cutting and burning all tops in the fall, and 
destroying all wild asparagus, aids in the prevention of rust. 

The Palmetto varieties are quite resistant and offer a 
solution of the rust problem in some localities. Careful 
breeding has given rise to several strains known as " Washing- 
ton asparagus" that are highly resistant. In dry climates 
dusting with sulfur 150 to 200 pounds per acre, about three 
weeks after cutting is finished and before the rust appears, 
is beneficial. It is best to sulfur early, and only when dew is 
present. 

In regions subject to rain, where the sulfur treatment is 
not applicable, three sprayings with sulfur-soda soap are 
recommended: first in July, other applications at intervals of 
three weeks. In New York three sprayings with Bordeaux 
mixture with rosin added as an adhesive gave a gain of 
$132.75 per acre. 

Minor diseases 

Anthracnose (CoUetotrichum sp.) is known by its numerous 
black acervuli borne in a blanched background upon the 



152 



Diseases of Economic Plants 



stem. It develops late in the season. The name Leopard- 
spot is strikingly suggestive for another disease that produces 
^ long, irregular spots, ashen in color, with 

dark borders. No treatment is known. 








BEAN 4^^ 

Pod-spot anthracnose ^^^-i««' i^^- ^97 
(Colletotrichum linde?nuthia7ium (S. & 
M.) B. & C). — First described in 1878 
in Germany, this disease is widely 
known and is especially destructive. It 
develops so rapidly that beans delivered 
to the cars for shipment in apparently 
healthy condition may, upon arrival at 
their destination, be quite badly spotted. 
The loss is often 20 per cent, and occa- 
sionally a total loss is reported. Upon 
the pods the disease appears as dark- 
colored spots, usually sunken, varying 
in size from 1-10 mm., or more if sev- 
eral spots coalesce. The border of 
the spot is often tinged with red, 
the center rust-colored. Old pod-spots 
overlying seeds within cause spots 
upon these seeds. The pod-spots are 
much more noticeable and unsightly 
upon light-colored than upon green 
beans. 

Similar spots are found upon the 
stems and leaves. They are especially 
noticeable upon young stems still 
blanched and upon the seed leaves. On 
Fig. 80. — Anthracnose older leaves they may appear upon the 

spots upon bean pods, ygi^s, blackening and killing them and 

After Stewart. ^i i r 

the leai. 

The wax varieties are especially susceptible, while lima 

beans are quite resistant. The Well's Red Kidney also 




Vegetable and Field Crops 



153 



shows valuable resistance. It is claimed that resistance is a 
dominant Mendelian character. 

The fungus is carried to fields largely by diseased seeds; 




Fig. 81, — Bean anthracnose upon stem and leaves of young 
plants. After Whetzel. 

by beans bearing the spots above mentioned. Such seeds 
result in infected seedlings which serve as a multiplying 
medium for the fungus and result in its spread and general 
attack upon the field. 



154 Diseases of Economic Plants 

In fields where the disease is well established upon stems 
and leaves the damage is great in loss of starch-producing 
power. Still greater loss follows from the spread of the 
disease to the pods, the unsighthness of the spotted pods 
greatly injuring their salability. 

Since the spores are spread only when they are wet, 
handling or disturbing the vines in any way while the dew 
or rain is still upon them should be avoided. Seeds already 
bearing the fungus, i. e., spotted seeds, should never be 
planted, since they not only raise sick plants, but also carry 
the disease to the field to infect other plants. One infected 
seed may carry contagion to the field. Spraying is not effec- 
tive. Since no remedy is at hand except the use of healthy 
seed, the greatest care should be given to this point. Home, 
fall-grown seed known to be free from disease is preferable 
to seed of unknown origin. If a few seeds known to be free 
from disease can be secured and multiplied in a special seed 
plot, they will give clean seed for future use. Clean culture, 
■the removal from the field and destruction of diseased stalks 
and plant parts, ehminates a source of spring infection which 
may be important. 

Rust ^^^' ^'^^ (Uromyces appendiculatus (Pers.) Link). — 
This rust may be recognized by its sori upon the leaves and 
occasionally upon other structures. The sori appear at 
first as blisters of pinhead size, covered by the epidermis of 
the plant. Later this covering ruptures and discloses a 
mass of spores the color of iron rust, or later in the season 
chestnut-colored, which fall away in quantity, smudging 
the leaf and spreading the disease. The upper side of the 
leaf opposite a sorus usually shows a spot, pallid, yellowish, 
lacking in true leaf-green color. Sori are sometimes found 
upon the upper surface, but not so frequently as upon the 
lower. 

Rust usually develops somewhat late in the season and 
therefore is not so destructive as are many of the other bean 
troubles, though in certain localities, e. g., in Virginia, the 
crop is sometimes completely destroyed. 



Vegetable and Field Crops 



155 



It is reported upon many species of true beans (Phaseolus) 
and upon related genera as Vigna, Falcata, Strophostyles. 
Where the disease proves destructive, the use of resistant 




"?' 



Fig. 82. — ■ Bean rust upon leaf and pods; note the numerous sori upon 
both surfaces. After Beach. 

varieties, clean culture, and the destruction of all wintering 
forms, is advisable. 

Blight ^^^ (Pseudomonas phaseoli EFS.). — Beans of va- 
rious kinds are subject to a blight which manifests itself 
upon the pod, leaf, or stem. It has been reported from 
various states, from Canada, is widely distributed, and 



156 



Diseases of Economic Plants 



often quite destructive. It was first observed by Beach in 
New York in 1892. 

Usually the leaves are the parts first attacked. Here 
large, translucent patches, brown in color, are produced. 
These spots later dry, become papery in texture, and rup- 
ture, leaving the foliage ragged and torn. Later infection 
spreads to the pods, which develop watery, ulcer-like spots 
without definite boundary, similar to those upon the leaves, 
though often amber-coated. Attack upon young pods kills 
them. 




Fig. 83. — Blight of bean leaves. After Fulton. 

This disease is carried over the season largely by infected 
seed and is conveyed from plant to plant in the field by 
insects. 

Diseased seed and seed from fields bearing the disease 
should be avoided, and clean culture, including the burning 
of all infected plant parts, should be practiced. The follow- 
ing list shows the variation in resistance, the least susceptible 
being placed first and the most susceptible last: Schindler's 
Round Pod Wax, Refugee Wax. Burpee's White Wax, 
Grenell's Rust-proof Golden Wax, Wardwell's Kidney Wax, 
Dwarf German Black Wax, Early Valentine. 



Vegetable and Field Crops 



157 



Stem-rot, pod- 
rot 1^' ^- 1^3 {Corti- 
cium vagnm). — 
This disease is 
manifest in three 
forms : 

1. Damping-off 
of seedhngs. See 
damping-off. 

2. Dry-rot of the 
stem. In this con- 
dition the tissue is 
dead, discolored, 
and dry-rotted at 
from 2-5 cm. above 
the ground. The 
rot extends to the 
pith and usually 
encircles the stem, 
and thus so weak- 
ens the plants that 
they are often 
broken by the wind. 
In any event the}^ 
soon wilt and die. 

3. As brown 
sunken areas upon 
pods, penetrating to 




Fig. 84. — Blight of the bean. After Halsted. 



and discoloring the seeds. The germination of the seed is not 

stopped by this 
attack, and a 
fruitful source 
of dissemina- 
tion is thus af- 
forded. Such 
seeds should be 

Fig. 85. — Blight upon bean seeds. After Clinton, avoided. 




158 Diseases of Economic Plants 

Downy-mildew ^^^' ^^^ (Phytophthora phaseoli Thaxt.). — ■ 
Downy-mildew is a northern disease regarded by Halsted 
as the most serious disease of the lima bean. It was first 
recorded by Thaxter in 1889. 

Upon the pods growths of dense, woolly-white, irregular 
patches appear. These consist of myriads of spore-bearing 
hyphse of the causal fungus, laden with their spores. The 
mildew also attacks young shoots, petioles, flower clusters, 
and leaves, causing them to develop in dwarfed, imperfect 
fashion and destroying their value. The spores are largely car- 
ried by nectar-seeking insects, which accounts for the preva- 
lence of flower infection. Spores are also carried by wind. 

Even in a season favorable to the development of the 
disease, thorough use of Bordeaux mixture, three sprayings, 
will insure the crop. The destruction of infected trash is 
advisable. 

Southern-blight (Sclerotium rolfsii). — The symptoms 
are wilting of the leaves, temporary recovery, yellowing, 
dying, and eventually dropping. The fungus usually at- 
tacks the plant just below the surface of the ground, in- 
vades the cambium, and destroys it. For further details, see 
pepper. 

Pod-blight ^^^ {Diaporthe phaseolorurn (C. & E.) Sacc, 
Phomopsis). — This destructive lima-bean blight was first 
recognized in New Jersey in 1891, and is now known gen- 
erally in the East, producing upon pods and leaves large, 
brown patches, with the pycnidia arranged in concentric 
circles. When the disease is prevalent, the pods fail to 
mature their seeds. 

Clean seed should be used and the plants sprayed with 
Bordeaux mixture. 

Drop ^^^ {Sclerotinia libertiana) . — This rot is reported to 
cause a reduction of 30 per cent in yield in some fields. Loss 
of nearly $3,000 is reported on one 30-acre field in Virginia. 
It may develop rapidly in transit, and thus cause secondary 
freight losses. Field refuse should be burned, and crop 
rotation practiced. See also lettuce. 



Vegetable and Field Crops 



159 



Minor diseases 

Orobanche is sometimes parasitic on beans. Sunscald ^^^ 
produces discoloration. Powdery-mildew {Erysiphe polygoni 
DC.) often gives a rusty color to the pods. Leaf -blotch 
{Cercospora cruenta Sacc.) occurs only upon the foliage as 
brownish patches, causing the 
leaves to fall away. The spots 
are large, angular, and limited 
by the veins. Leaf-spot {Isar- 
iopsis griseola Sacc.) is chiefly 
limited to the foliage, produc- 
ing small, angular spots, over 
the under surface of which the 
fungus forms a gray, moldy 
covering. It has been ob- 
served in many states, and is 
most injurious in the South. ^^'' 
Wilt due to Pseudomonas sol- 
anaceariim has also been re- p 
ported. Root-knot (nema- 
todes) is injurious in some 
localities. Streak. — Dark 
spots occur on stems, leaves, 
and pods. The cause is un- 
known. Mosaic ^^^ in general 

character resembles tobacco j-^^ g^ _ j^.^^_b^^^ p^^^ ^^^^^. 
mosaic. It appears to be of ing pod-blight. After Halsted. 
wide distribution and to be 

communicated through the seed. Resistant strains should 
be grown. 

BEET, CHARD, MANGOLD, MANGELS 

Cercospora Leaf-spot i9i~i94 (^Cercospora heticola Sacc). — 
This, one of the several leaf-spots upon the beet, is very 
widespread in the eastern and middle states. Very few 
fields are entirely free from it. It occurs upon all varieties, 
but is especially injurious to the sugar beet. 




160 Diseases of Economic Plants 

The round, brownish, purple-bordered spots turn ashen 
in the center, and, when mature, often become so thin and 
brittle as to drop out, leaving ragged holes. The sporiferous 
hyphse upon the spot centers may be seen with a good lens. 

These spots frequently destroy the greater part of the 
green tissue of the leaf, and thus its value to the plant as a 
sugar producer, or even cause the leaves to die, in which 
event they blacken and remain standing nearly upright upon 
the crown. The death of the older leaves causes the crown 
to elongate, suggesting the name "pineapple disease." 
Dry weather followed by a damp spell favors the disease. 
Infested refuse in manure may serve to spread the leaf-spot 
but beet tops made into silage do not carry contagion. 

Sprayed plants in New Jersey gave a much cleaner foliage 
and yielded 480 pounds of root as against 380 pounds from 
the unsprayed plants from an equal area, a gain of nearly 
26 per cent. While partial control may thus be had by 
spraying, the cost may not, however, be justified. Crop 
rotation and deep fall plowing should be practiced. 

Curly-top. ^^^' ^^^' -^^ — The first symptom appears in the 
inner leaves, which curl inward from the entire margin toward 
the midrib. Soon the veins become knotted on the dorsal 
surface. Later, the entire plant is stunted and shows similar 
changes; whole leaves curl tightly and the petioles remain 
short and become bent. The roots develop an abnormal 
number of fine rootlets, leading to the common name "hairy- 
root." (See also p. 162.) They are also tough and some- 
times present a blackened area or cavity within. Curly-top 
occurs annually on sugar beets in Colorado, Utah, Idaho, and 
California, and in fact in all states west of Nebraska where 
sugar beets are grown. In some years thousands of acres are 
completely destroyed, the total loss during the last sixteen 
years being estimated at $16,000,000. Even though the beets 
grow to fair size, impurities lower their value for sugar 
production and their seeding power is injured. The disease, 
however, is not seed-borne. As to the cause, but little is 
definitely known beyond the fact that this disease can be 





ft 



Fig. 87. — Curly-top. After Boncquet. 



162 Diseases of Economic Plants 

conveyed by grafting, but otherwise develops only after the 
sting of a leaf hopper {Eutettix tenella) that has been in con- 
tact with beets affected with curly-top. Bacillus morulans 
Bone, has been associated with curly-top, but its causal 
relation not demonstrated. 

Root-rot ^^^ {Corticium vagum) . — Beets affected with 
this rot usually show first attack at the bases of the outer 
leaves, which turn black. The stalks weaken and allow 
the leaves to fall prostrate, though they do not lose their 
color at once. The disease thence passes into the crown, 
turning the involved parts brown and later leading to crack- 
ing of the root. In this condition the mycelium of the 
fungus is clearly evident in the cracks. Eventually the 
whole top may rot off. The spread is rapid from plant to 
plant in the field. Dry or cold weather may so retard the 
invasion that the plant can recover if not too badly affected. 

The disease is probably the same that has been destruc- 
tive to sugar beets in Germany. It has been reported from 
several places in the United States. 

Air-slaked Hme, 60 to 70 bushels per acre, has been recom- 
mended. 

Phoma Root-rot ^^^ (Phoma hetce (Oud.) Frank.). — Upon 
the roots a shrunken, coal-black discoloration, extending 
sometimes quite to the center, indicates the presence of this 
dry rot. No disagreeable odor attends the rot. Upon the 
affected surface pycnidia appear as very minute pustules. 
Upon the leaves this same fungus forms large, circular, 
dead spots. The disease may also appear on seedlings, caus- 
ing damping-off. 

All infected leaves should be removed from the roots 
before placing in storage. 

Root-knot and Hairy-root (nematodes). ^^^' ^^^ — Two spe- 
cies of nematodes affect beets, one of which produces root- 
knot, the other hairy-root, both of which are quite destruc- 
tive. Root-knot, due to nematode-infection, is discussed on 
p. 24. Hairy-root shows first symptoms, as the hot season 
begins, in a wilting, yellowing, and dying of the outer leaves, 



Vegetable and Field Crops 163 

and dwarfing of the inner leaves. Dense masses of fine root- 
lets develop below ground, giving rise to the common name. 
The really distinctive character is the presence of numerous 
yellowish, beadlike objects, a little over a millimeter long, 
clinging to the rootlets. This disease has been very destruc- 
tive in Europe, and, introduced into the United States prior 
to 1907, is established in several districts in the West. Fol- 
lowing is a partial list of plants known to be susceptible to 
hairy-root. Those marked with a * are highly susceptible. 
Alfalfa, allseed, barley, bean, dwarf pea, lima bean, garden 
beets,* sugar beets,* Brussels sproutsj* cabbage,* Chinese 
cabbage,* cauliflower,* celery, crimson clover, white clover, 
corn, cress,* dandelion, green foxtail, hemp, hops, kale,* 
kohl-rabi,* lentils, yellow lupine, annual meadow grass, 
tall meadow oat-grass, mustard,* oats, parsnip, garden pea, 
sweet pea, pink, potato, radish,* rape,* rutabaga,* rye, 
sorghum, spinach, sunflower, timothy, turnip,* vetch, wheat. 

A rotation of four or five years with nonsusceptible crops 
is the only safe procedure with infected land. Small areas of 
local infection may })e eliminated by a heavy application of 
unslaked lime well mixed into the soil. 

Black-root "^"^ (Rheosporangium aphanidermalus Eds.). — 
Black-root occurs on both radish and beet, causing damping- 
off and a browning or blackening and often death of the root. 
Disinfection of seed is advisable. 

Damping-off. — Damping-off of seedlings near the surface 
of the ground soon after they come up, often before thin- 
ning, is a frequent cause of loss. The leaves yellow, the 
roots turn brown, and the plants topple over and die. This 
is, in some instances, due to the usual causes of damping- 
off, Corticium, Pythium, Phoma, but sometimes to a heavy 
crust formed upon the soil, thus preventing the safe emerg- 
ence of the seedling. 

Minor diseases 

Scab ^^^ {Actinomyces scabies) resembles closely the scab 
of the Irish potato. It usually covers more completely 



164 Diseases of Economic Plants 

the surface of the beet than in the case of the potato, and 
tends more to form corky growths upon the surface than 
to make deep cavities. Beets should not be grown upon 
land known to be infested with the potato scab or to have 
borne a badly infected crop of beets. See also potato scab. 

Bacterial Leaf-spot ^^^ (Pseudomonas aptatum (B. & J.). 
— The leaves in this disease bear irregular, dark brown 
or black spots, 1 mm .-3 cm. in diameter, chiefly upon the 
petiole, midrib, and larger veins. Occasionally the dis- 
coloration extends along a vein for some distance, and the 
tissue on either side becomes brown and dry. 

The disease was first observed by Townsend in Utah and 
Colorado, and its bacterial origin was demonstrated by 
Brown. 

Rust {Uromyces betce (Pers.) Kiihn) has long been known in 
Europe, where it was studied as early as 1869. It is occa- 
sionally met in some of the western states and has been 
reported as injuring the beet in market gardens in California. 
It is recognized by the characters of the true rusts, i. e., 
blisterlike sori. 

Removal of the leaves bearing the spring stage and spray- 
ing with Bordeaux mixture has been recommended. Af- 
fected leaves used as feed may carry the disease through 
the manure to plants of the following season. 

White-rust (Albugo hliti (Biv.) Ktz.). — The sori are 
blisterlike, as in the true rusts. The rupture of the epidermis 
releases masses of snow-white spores. 

Soft-rot ^^^ {Bacterium teutlium Met.) was prevalent in 
Nebraska in 1904. Leaf -scorch. -^^ — The leaves blacken 
and die, and the roots are small, discolored, and poor in 
sugar content. Crown-gall and Root-tumor (Urophlyctis), 
Downy-mildew (Peronospora) , and Drop {Sclerotinia) cause 
some loss. 

BROCCOLI. See cabbage. 

BRUSSELS SPROUTS. See cabbage. 



Vegetable and Field Crops 



165 



BUCKWHEAT 

Blight ^^"^ (Cortidum vagum), causing death of plants in 
large areas in the field, was noted in North Carohna. Leaf- 
spot (Septocylindrium rufomaculans (Pk.) P. & C.) is reported 
as diminishing the yield in Connecticut. Powdery-mildew 
{Erysiphe polygoni) is of slight importance. 



CRUCIFEROUS CROPS: CABBAGE, BRUSSELS SPROUTS, 
CAULIFLOWER, COLLARD, TURNIP, KOHL-RABI, 
KALE, RAPE, RADISH, BROCCOLI, RUTABAGA 

These crop plants are of close kinsliip and are subject, 
essentially, to the same diseases. The more important of 
these are internal parasites from the soil, hence spraying is 
of less benefit than with 
other crops. 

Black-rot -^^--os- 228. 319, 340 

{Pseudomonas campestris 
(Pam.) EPS.). — Not only 
does black-rot destroy the 
current crop, but since its 
causal germ remains in the 
soil, it seriously endangers, 
if it does not quite prohibit, 
the subsequent use of the 
same field for susceptible 
crops. Its damage to cab- 
bage in a single season in 
two counties in Wisconsin 
was estimated at between 
$50,000 and $60,000. A 
large per cent of the dam- 
age to cabbage in storage Fig. 88. — Cabbage leaf showing an 
is also attributable to this incipient stage of black-rot. The 

disease. Cabbage, kale, ?^'^^'^' ^^^^^ ^^*^"". ^* ,*^^ ^""^l^^ 

, ,. Ill 1 • the veins, is progressing toward the 

rape, broccoh, kohl-rabl, base of the leaf . After Stewart and 

Brussels sprouts, collards, Harding. 




166 



Diseases of Economic Plants 



turnips, rutabagas, radish, black mustard, charlock, and 
other members of the cress family are affected. 

Black-rot was first noted on turnips in 1892 in Iowa, and 
on cabbage in 1895 in Wisconsin, and is now very dis- 
astrous in its effects in practically all sections of the 
United States east of the Mississippi River, as well as in 
the more western states. 

Infection arises from the 
causal bacteria which are 
often present in the soil from 
preceding years. These bac- 
teria gain access to the drops 
of water at the water pores 
on the leaf edge. The first 
sign of the disease appears 
as a blackening of the veins 
upon the edges of the leaves. 
The affected region rapidly 
enlarges, the blackening ex- 
tending toward the stalk, 
and throughout the vascular 
system. Soon this blacken- 
ing reaches the stem of the 
plant and proceeds up and 
down the stem, thus gaining 
Portion of cabbage stem entrance' to other leaves, 

finally reaching the entire 
plant. Usually many leaves 
are infected simultaneously. Affected leaves soon yellow 
and wilt, owing to the obstruction of the water channels, 
then dry, become parchment-like, and fall to the ground. 
General infection of the plant is followed by death. Reliable 
diagnostic characters are the blackened vein areas of the leaf, 
blackened veins as seen in cross sections of the leaf stalk or 
of the stem of the plant. Other rots may supervene, giving 
offensive odors. If plants with the smallest amount of dis- 
ease are placed in storage, the disease continues to develop, 




Fig. 89. 

showing blackened veins 
drawn after Russell. 



Re- 



Vegetable and Field Crops 



167 



resulting in complete loss. The bacteria may travel upon 
seed from diseased localities, infect the young plants, and 
initiate an attack in a new locality. Plants shipped across 
the country may also carry infection. 

The disease may be carried from field to field in any 
plant part or in infected soil, upon tools, feet, etc., and espe- 
cially in manure that has become infected by the use of 




Fig. 90. — Cauliflower affected with black-rot. 
Original. 

diseased plants as feed. To avoid carrying contamination 
to near-by fields all the precautions suggested under soil 
diseases must be employed. 

With infested land the only recourse is such crop rotation 
as will avoid the planting of a susceptible crop for a period of 
several years. Just how long the bacteria can remain alive 
in the soil is not known. In practicing crop rotation for 
elimination of this pest all cruciferous weeds, mustard, shep- 
herd's purse, etc., should be avoided, since they are sus- 



168 



Diseases of Economic Plants 



ceptible and harbor the disease just as effectively as would 
cabbage. ■ 

Since the seed may carry the bacteria, it is well to soak 
them for fifteen minutes in formalin, one teaspoonful to a 
half pint of water, to kill these germs and thus avoid in- 
troducing the disease into new localities. If this had been 

done in earlier years, many 
counties now so infected as to 
prohibit cabbage culture would 
.still be free from this pest. 
Resistant varieties will do 
much to solve the problem. 

The cauliflower is affected 
in muijh the same way as the 
cabbage. Local infection in 
the head often produces the 
effect shown in Fig. 90. 

Club-root 208-211. 227 ^pi^g_ 

modiophora brassicce Wor.). — 
Club-root is practically of 
world-wide distribution, and 
destructive to cabbage, kale, 
cauliflower, turnip, rutabaga, 
collards, Brussels sprouts, 
radish, stocks, candytuft, sweet 
alyssum, and upon wild crucif- 
erous plants, shepherd's purse, 
peppergrass, pennycress, black 
mustard, charlock, false flax, 
hedge mustard. It may readily be recognized by the en- 
larged growth of either the main root or the lateral roots, or 
both, as shown in the accompanying figure. It cannot be 
confounded with any other disease unless that caused by 
eel worms (nematodes), and from this it may easily be dis- 
tinguished by the larger club-root galls. 

These swellings may be noted in the seed bed, though they 
are usually overlooked until they enlarge in the field. They 




Fig. 91. — Cabbage club-root. 
Original. 



Vegetable and Field Crops 169 

so diminish the vigor of the plant that it assumes a sickly 
appearance, ceases to develop, and fails to head. The 
affected parts usually succumb to offensive secondary rots, 
the causal organism is released, and the soil is thus infected. 

The proof of the parasitic origin of this disease was made 
by Woronin in 1873, after three years of intensive study. 

In general the precautions against its spread are those 
suggested under the general heading of soil diseases. All 
diseased refuse is infective, as is also manure to which it 
has had access. Fields which are diseased remain so for 
several years; therefore rotation to nonsusceptible crops 
should be followed. Seedlings should be examined care- 
fully to guard against the use of plants from an infected 
seed bed, and special care should be taken to avoid infecting 
the seed bed with soil, manure, or refuse. Air-slaked stone 
lime, 75 bushels per acre, applied each year some weeks be- 
fore planting, has given beneficial results. In New York, 
where 90 bushels of shell lime were applied per acre, an ex- 
cellent crop was grown, while upon untreated soil only 60 
heads were cut from 472 plants. The Hollander and the blue 
or red varieties of cabbage are said to show some resistance. 

Root-knot (nematodes) . — Root-knot in some respects 
resembles club-root, but with smaller swellings. It is com- 
mon on crucifers. 

Black-leg ^^^' -^"^ (Phoma lingam (Tode) Desm.). — Great- 
est injury is done to cabbage and cauliflower, less to other 
crucifers. Dark, sunken areas occur on the stems near the 
ground; gradually the stem, and later the plant, dies. Spots 
may also appear on leaves or petioles. The presence of pyc- 
nidia in the spots is the really distinctive character. The dis- 
ease is important chiefly in the East and North, though it has 
been reported from the South and extreme West, as well as 
from Europe and Australia. Infection may be carried or main- 
tained by diseased refuse or on the seed. Seeds should be dis- 
infected (pp. 240, 449), and healthy soil used for the seed bed. 

Black-mold {Alternaria hrassicw (Berk.) Sacc). — Upon 
the cabbage, cauliflower, and collard, particularly in the 



170 



Diseases of Economic Plants 



South, this mold is quite destructive both in the field and in 
storage. The affected spots are nearly black, circular, 
marked concentrically, and are not definitely bordered, i. e., 
they shade off gradually into the surrounding healthy tissue. 




Fig. 92. — Black-mold on collard as seen from 
upper side of the leaf. Original. 

They enlarge sometimes to 2-3 cm. in diameter. The tissue 
dries, becomes brittle, and often falls away, leaving ragged 
holes. 

In many instances the plants die or fail to mature. In 
storage the spots continue to enlarge, and it is here that the 
greatest loss occurs. Storage houses should be disinfected 
with Bordeaux mixture, and temperature and ventilation 
regulated as suggested under soft-rot, p. 172. 

Drop ^^^ (Sclerotinia lihertiana). — This malady is dis- 
cussed under lettuce. Upon the cabbage, rape, cauliflower, 



Vegetable and Field Crops 



171 



and radish it may be recognized by the cotton-Uke mycehum 
and the black sclerotia which appear in advanced stages of 
disease. It is particularly troublesome in the Southern 
states. 

A form of this rot is described by Hedgcock as closely 
resembling black-rot, except that it is more watery. Often, 
too, the petioles rot away 
at the base and the leaves 
droop. The general prac- 
tices recommended under 
lettuce drop will apply. 

Downy-mildew {Pei^- 
onospora parasitica (Pers.) 
De Bary) . — Downy-mil- 
dew produces the char- 
acteristic downy patches 
of sporophores upon the 
lower surface of the leaves, 
much as is the case of the 
grape. Seen from above 
the diseased spots are an- 
gular, limited by the veins, 
pale yellow, and the tissue 
is somewhat shrunken. 

The disease is common 
to cabbage, collard, cauli- 
flower, turnip, radish, and 
many other members of 
the cress family. It has 
been reported in several 
states, notably Ohio, New Jersey, New York, Delaware, 
Maryland, South Carolina, North Carolina, West Virginia, 
and in Europe and Australia. Though it is seldom of impor- 
tance in the field, it occasionally does damage in the seed bed. 

Spraying the plants in the seed bed with Bordeaux mix- 
ture will hold the disease in check. Diseased plants should 
be destroyed by fire as soon as the bed has been used. 




Fig. 93.- 
spotted 
Original. 



Seedling cabbage plant 
with downy-mildew. 



172 Diseases of Economic Plants 

Yellows, Wilt ™'^' "''^' ^-'^ (Fusariuin conglutinans WolL). — 
This wilt of cabbage is destructive through a large territory, 
particularly in the Southern states, and at least as far 
north as Minnesota. As high as 90 per cent of loss has 
been reported. 

The chief symptom is yellowing and falling of lower leaves, 
and eventually all of the loaves except those of the head. 
This character may be strongly emphasized upon one side 
of the plant or even upon one side of single leaves. Affected 
plants are retarded in growth and often die. After death 
abundant pink acervuli are seen. Cross section of an 
affected stem shows the wood ring to be darker than 
normal. 

In treatment the same methods should be followed that 
are suggested for cabbage black-rot; especially should in- 
fested land be avoided, and the young plants grown in healthy 
soil. The Volga and Houser are the most resistant of the 
older varieties. The Wisconsin Hollander is a disease re- 
sistant variety developed by selection. 

White-rust (Albugo Candida (Pers.) Ktz.). — White-rust 
upon radishes often causes curious malformation of the 
flowers and pods, which become overgrown and distorted; 
often a flower is five times its normal diameter and is color- 
less. Chief damage is thus done to the seed crop, which 
may be quite ruined by this attack upon the flowers. It is 
quite general on crucifers, but really injurious only to the 
radish. 

Burning of all infected trash is the best preventive. 

Soft-rot (Bacillus carotovorus) , (See carrot.) — This is a 
soft, slimy, wet decay affecting any part of the plant, and 
spreading rapidly throughout. Wounds are necessary to 
infection. Much injury occurs in the field, but the greatest 
loss is in storage houses. Here the temperature should be 
kept a degree or two above freezing, and good ventilation 
secured. Wounds should be avoided in so far as possible, 
and the crop dried before storing. 



Vegetable and Field Crops 173 

Minor diseases 

Malnutrition. -'^^ — Leaves, yellowish between the veins 
and at the margins, are thickened and brittle. The cause 
chiefly rests in use of too much mineral fertilizer and lack of 
humus. 

Powdery-mildew (Erysiphe) ; Damping-off (various fungi) ; 
Ring-spot {Mycosphcerella) do but small harm. Phoma-rot, 
Black-root (see beet) and a Macro sporium leaf -spot are 
reported on the turnip. Pale-spot {Cercosporella alhomacu- 
lans E. & E.) is also common on leaves of turnips. An- 
thracnose ^^^ {Colletotrichum higginsianum Sacc.) occurs on 
stems and pods of turnip, and is especially injurious on 
young plants. Leaf-spot -^"^ (Pseudomonas macuUcolum 
McC.) occurs on leaves of cauliflower and cabbage. The 
spots are brown to purplish-gray, 1-3 mm. in diameter. The 
leaves become puckered, and when badly diseased, fall off. 

CANTALOUPE. See p. 178. 

CAPER 

White-rust {Albugo) and Powdery-mildew (Erysiphe) are 
recorded, but do small harm. 

CARROT 

Soft-rot ^^^' ^^^ (Bacillus carotovorus Jones). — In Vermont 
serious loss from rotting of carrots was reported to the Exper- 
iment Station in 1898. Investigation by Jones showed it to 
be due to bacteria and that numerous other crops — namely, 
turnip, rutabaga, radish, salsify, parsnip, onion, celery, 
hyacinth leaves, and the fruit of tomato, eggplant, and 
pepper — were susceptible to the same disease. 

Rot begins in the field and seriously increases during stor- 
age. The initial attack is either at the crown or root tip, 
from which points it proceeds rapidly through the core, 
which becomes softened and somewhat browned with a rather 
sharp boundary between diseased and healthy tissue. 



174 



Diseases of Economic Plants 



Fields known to be infested should be relieved of sus- 
ceptible crops by suitable rotation. Manure which may 

have become infested in any way, 
e. g. by feeding diseased crops to 
stock, should be avoided. Drying 
of the roots kills the causal or- 
ganism, as does also exposure to 
sunlight. Drying in the light is 
therefore equivalent to surface dis- 
infection and serves to reduce the 
damage. Storage below 10° C. (50° 
F.) gives best results. 

Drop (Sderotinia) , see lettuce,, 
and Southern-blight (Sclerotium) , 
see pepper, are of some im- 
portance. 

CASTOR-BEAN 

Wilt (Pseudomonas solanacearum) 
(see p. 230) does considerable dam- 
age, dwarfing the plants, causing 
typical wilt, and finally death of 
many plants. 

Gray-mold ^^^ {Sderotinia ricini, 
Godf., Botrytis) of flowers, buds. 
Fig. 94. — Carrot showing and pods in some cases affects 50 
soft-rot; shaded portions to 90 per cent of the plants with a 
represent the rotted part ^^^ j.^^, Diseased tops should be 




of the root, 
after Jones. 



Redrawn 



cut and Bordeaux mixture used. 



CAULIFLOWER. See cabbage. 



CELERY, PARSLEY, PARSNIP 

Late-blight "^^ (Septoria petroselini Desm.). — In Italy late- 
blight was first reported in 1890; in the United States in 1891. 
A loss of 1950 carloads and a money loss of $550,000 was 



Vegetable and Field Crops 



175 



estimated in California in 1908; in Michigan in 1915 a loss of 
more than a million dollars. A cut in price of 5 to 10 cents 
per crate is common when the bunches are only slightly 
disfigured. The disease occurs on celery, also on parsnip and 
parsley. 

In its early stage it consists of leaf spots; in later stages, 
the infection of the leaf becomes general, numerous black 
pycnidia are scattered upon all parts and even upon the 




Fig. 95. — Celery leaf infected with Septoria. After Coons. 



blanched petioles. In extreme cases wilting of the leaves and 
destruction of the plant follows. After the celery is put in 
storage the disease may still progress and do great damage, 
rotting off the leaves and forcing early marketing. Late- 
blight is often found in the seed bed, and is probably carried 
by the seed, since the pycnidia are abundant upon the seed- 
ing stalks and fruit. 

Seeds should be disinfected and the seed bed rotated. If 
the disease has been troublesome in preceding years, the 



176 Diseases of Economic Plants 

plants in the seed bed should be sprayed with Bordeaux mix- 
ture as soon as they are above ground, and once or twice a 
week thereafter until transplanted. If the disease develops 
in the field, the crop should be sprayed with Bordeaux mix- 
ture at ten-day intervals. The following is taken from a 
Michigan publication in 1915: 

One-sixth acre (from which accurate returns were 
kept) sprayed with a knapsack sprayer at a total ex- 
pense of $2.00 for labor and material gave 125 crates 

(10x10) fine quality at $1.00 value $125.00 

A similar unsprayed area gave 18 crates poor quality 

at 50c 9.00 

Excess return of sprayed plot $116.00 

Cost of spraying 2 . 00 

Net gain $114.00 

On the rest of the acreage, at an expense of not more than 
$12.00, Mr. Joldersma saved a crop valued at about $1500. 

To minimize loss no diseased plants should be stored. If 
storage is imperative, badly infested leaves should be picked 
oflf, and in extreme cases the plants should be dipped in a 
fungicide (ammoniacal copper carbonate) before they are 
stored away. 

Early-blight, leaf-spot, ^^^ (Cercospora apii Fr.). — Leaf- 
spot is common on celery, parsley, and parsnip in both 
Europe and America. It is reported from California to New 
Jersey. In Florida in 1906 it is said to have injured 80 per 
cent of the crop. The crop is largely reduced, and the un- 
sightliness of the spots injures the salability of the product. 

The spots appear first upon the outer, older leaves as 
pale yellowish areas, showing from both sides of the leaf. 
They are irregular with slightly raised border and are an- 
gular in outline, owing to their limitation by the veins. They 
seldom exceed 3-6 mm. in diameter unless by the coalescence 



Vegetable and Field Crops 177 

of several spots. The spots soon become brown, and the 
central part turns ashen-white and is seen by the aid of a 
hand lens to bear numerous hyphse. The leaves may bear so 
many spots as to appear as though scorched, and often death 
results to the entire plant. 

The disease spreads most rapidly in damp, warm weather. 

Marked difference in varietal resistance was reported by 




Fig. 96. — Early-blight of celery. Original. 

Tracy as early as 1885, the Boston Market and Golden 
Heart suffering much, while the White Plume was but slightly 
injured. 

All plants showing a trace of disease should be rejected. 
Healthy plants from infected lots may with advantage be 
dipped in Bordeaux mixture to cleanse them of adhering 
spores. Spraying with ammoniacal copper carbonate or 
Bordeaux mixture is effective. Treatment should be begun 
before the disease appears, i. e., in the seed bed, and con- 



178 Diseases of Economic Plants 

tinued at ten-day to fourteen-day intervals throughout the 
growing period. All spore-bearing refuse should be burned. 

Minor diseases 

Leaf-spot {Phyllosticta apii Halst.). — A dull brown, cir- 
cular pycnidia-bearing patch, not to be confused with the 
light, ashen-colored, angular Cercospora spot, is charac- 
teristic. Soft-rot (Bacillus carotovorus) consists of a soft, 
light-brown rot of the central bud, sometimes of the leaf 
or leaf stalks. It occurs on celery, also on parsley, and 
is probably identical with the carrot soft-rot. Rust {Puc- 
cinia hullata (Pers.) Wint.) has not yet been destructive in 
America. Damping-off due to Sclerotinia, Rhizoctonia, and 
Fusarium have caused much loss in the South on both celery 
and parsley. See also p. 19. Pithiness. -^° — The stalks and 
hearts are pithy, a condition attributed to the parent plant 
and heredity, not to parasites or environment. As high as 
30 per cent of pithy plants have resulted from certain lots of 
seed. Proper rogueing of seed plants is recommended. Scab 
due to Phoma apiicola Kleb. consists of rotting of the roots, 
leaving the plant with a conical rotten base. 

CHARD. See beet. 

CHIVE. See onion. 

COLLARD. See cabbage. 

CUCURBITS: CUCUMBER, ^39 MUSKMELON, MELONS, 

WATERMELON, PUMPKIN, SQUASH 

Downy-mildew ^^^ (Peronoplasmopara cubensis (B. & C.) 
Clint.). — Downy-mildew first shows its presence by yellowish 
angular spots, 3-6 mm. in diameter, upon the leaves as seen 
from above. These appear first upon the older leaves at 
the center of the plant. The spots become more distinct, 
enlarge, increase in number, and soon the whole leaf be- 
comes pale, sickly, and dies. If the weather is moist, the 



Vegetable and Field Crops 



179 



characteristic white hyphse and spores tinged with purple 
may be seen on the under sides of the older spots. The 
disease progresses to the younger leaves, slowly in dry or 
cool weather, but very rapidly in warm, wet weather. The 
field is soon reduced to a mass of dry, dead leaves. 




Fig. 97. — Spots of downy-mildew upon cucumber leaf. After Orton. 



The mildew was first described in 1868 from Cuba. In 

1889 it attracted attention in the United States (New Jersey, 
Florida, and Texas) and in Japan. Since that time it has 
been destructive in many states. The loss in Wayne County, 
Ohio, alone was estimated at $45,000 in one season. 

It grows upon muskmelons and cucumbers in most de- 
structive form and is less injurious to squash, pumpkin. 



180 



Diseases of Economic Plants 



watermelon, gourd, and other cucurbits. The fungus winters 
out of doors in the South and in the greenhouse in the North 
and spreads thence to the fields annually if weather condi- 
tions are favorable. 

This disease is often injurious to cucumbers under glass 

as well as in the field. 
It is well to sulfur 
the greenhouses 
thoroughly when not 
in use and to clean 
and whitewash all 
walls and wood in 
order to kill any fungi 
present. Should the 
disease appear, spray 
at once as in field 
practice. For direc- 
tion for field spraying 
see cucurbit spray- 
ing, p. 191. 

Anthracnose ^^^' ^^^' 
^^^ {Colletotrichum la- 
genarium (Pers.) E. 
& H.) . — This disease 
was first noted in 
1867 in Italy, and 
is now common in 
Europe and the 
United States, occur- 
ring on cucumber, 
muskmelon, water- 
melon, gourd, and a 




Fig. 98. — Portion of watermelon showing 
effect of anthracnose. After Sheldon. 



few other related plants. The loss is severe on the three crops 
first named, and is of more importance to cold-frame crops 
and crops under glass than to field crops, though it some- 
times does cause almost total loss of the latter. Upon the 
leaf, circular, not angular, spots occur which, instead of 



Vegetable and Field Crops 181 

yellowing, turn brown, die, and become ragged in appear- 
ance. Tendrils, buds, and petioles turn black and die. Upon 
the stems and fruit the spots are sunken and bear numerous 
acervuli. Its most conspicuous form is upon the fruit at any 
age, especially at maturity. Here very characteristic sunken 
spots with pink centers, much like the bean pod-spot, are 
produced. Upon old melons they do but slight injury, but to 
young fruit the attack is often fatal. A bitter taste is often 
imparted to the fruit. The disease is spread through the 
field by rain and surface drainage water, and winters in the 
field. It is probably carried to new fields by the seed. 

Spraying with 4-4-50 Bordeaux mixture is recommended. 
Clean seed should be used, or the seed disinfected. It is also 
well to destroy infective refuse and to practice rotation. 

Wilt "-^^ (Fusarium vasinfedum Atk.) — The melon wilt 
not only destroys the growing crop, but prevents the suc- 
cessful culture of melons upon the field in question in suc- 
ceeding years. It is less frequently met on the muskmelon 
than on watermelons. A sunilar wilt of squash is said to 
be caused by a different Fusarium. The wilt has spread 
rapidly during the past decade, and is now known from the 
Atlantic to the Pacific, and from the Gulf to Iowa. 

The first symptom appears in the leaves which droop as 
though they were suffering from want of moisture. The 
leaves and runners wilt rapidly, and this is soon followed by 
the death of the entire plant. 

Upon cutting the main tap root across near the surface 
of the ground, the wood presents a yellow color, making a 
distinct contrast with the white wood of the healthy plants. 
This one character, taken together with the wilted appear- 
ance of the vine, enables recognition of the true wilt. The 
further fact that a field once infested shows the same disease 
in succeeding years in the same or in extended areas is an 
additional recognition mark. 

Its spread may occur in the ways mentioned under soil 
diseases and in particular through the use of infested manure. 

To restrict it to its present confines, crop rotation should 



182 Diseases of Economic Plants 

be practiced and infested soil should not be replanted to 
melons until the wilt fungus is largely diminished in quantity. 
This will probably take more than four years, possibly eight 
or ten years, and even at the end of that time it is best to 
try a few hills before planting the whole field to melons. 
Cattle should not be allowed to pasture upon diseased vines 
and thus spread the wilt through manure. 

The practice of raising cowpeas after melons leads to the 
presence of some melon vines in the cowpea hay, and this 
likewise leads to the presence of the causal fungus in the 
compost heap. Manure so exposed to infestation should never 
be placed on land which is still free from the germ, or which 
is to be used for melon culture, since this is certain to spread 
the wilt. 

There is no objection to the use of stal^le manure which 
does not contain the fungus, but experience has shown 
that when the wilt once gains entrance to the compost heap 
or barnyard, it remains there for years, and all of the manure 
taken out of such a yard is likely to spread the disease. Hence 
it is exceedingly dangerous, in regions where the wilt pre- 
vails, to use any stable manure on the field where melons are 
to be planted. 

Varieties resistant to this disease have been developed by 
the United States Department of Agriculture by crossing the 
citron, which possesses high resistance, with the watermelon, 
and then by practicing selection to attain the desired 
edibility. 

Wiit^^^o, 540 (Bacillus tracheiphilus EFS.). — The cucum- 
ber, muskmelon, pumpkin and squash are susceptible but 
not the watermelon. 

The disease has been reported from many states — among 
them Nebraska, Wisconsin, Maryland, Massachusetts, 
Indiana — and is presumably present in many others. 

The attack in first stages causes the vine to droop through- 
out its length. This is followed by death. The infection is 
spread by insects, particularly beetles on which the bacteria 
probably hibernate to some extent. 



Vegetable and Field Crops 183 

Spraying with strong Bordeaux mixture, 4-5-50, with 
two pounds of lead arsenate powder added is recommended. 
Diseased vines should be pulled and burned, rotation prac- 
ticed, and in general the suggestions given under soil dis- 
eases (p. 26) should be followed. 

Timber-rot '^^^ {Sderotinia libertiana FcL). — Upon cucum- 
^^y. bers and other cucurbits under glass this disease occasions 
serious loss. It is rare out-of-doors. The first indication 
is the appearance of a dense mass of white mycelium near 
the nodes of the stem which is still green. As the disease 
progresses the stem shrinks and yellows, the softer parts 
decay, and the stem finally dries up. In the interior of af- 
fected stems the white mycelium, and later near the nodes 
or in the external mycelial masses, smooth, slender, black 
sclerotia may be found. The germination of the sclerotia, 
described under lettuce drop (p. 197) results in immense 
numbers of spores. These falling upon dead tissues germinate 
and form a mycelium which attains such vigor as to enable it 
to attack healthy tissue and rapidly destroy it. 

To control this disease all infected plants should be de- 
stroyed by fire before they have had opportunity to form 
sclerotia, and the places from which they are taken should 
be sprayed with a heavy application of some fungicide. 

Leaf-blight "^^ {Alternaria brassicoe (Berk.) Sacc. var. 
nigrescens Pegl.). — Leaf-blight and downy-mildew are the 
most destructive diseases of the muskmelon in this country. 
In Florida, in some seasons, nearly the whole commercial 
crop is lost. Much damage has been reported from Ohio, 
Indiana, and Colorado. 

Leaf -blight begins as small, round, brown spots usually 
marked by concentric rings. In the centers of these spots 
the hyphse develop a moldlike growth. The spots enlarge 
to a centimeter or more, coalesce, dry, and cause the leaf to 
curl and shrivel at the margin. The petioles and veins are 
also affected. Ripening of the melons is hastened, but the 
quality is destroyed, the fruit becoming soft, wilted, insipid, 
and valueless. 



184 



Diseases of Economic Plants 




Fig. 99. — The Pollock muskmelon vines adjacent to those shown 
in Fig. 100, showing complete resistance to the leaf-blight. 
After Blinn. 




Fig. 100. — Miiskmelon showing complete death of vines attacked 
by leaf-blight. After Blinn. 



Vegetable and Field Crops 



185 



If melons be repeatedly grown upon the same field, the 
disease increases year by year; hence rotation should be 
practiced, and resistant varieties should be used. A promis- 
ing resistant variety has been reported by Blinn. Spraying 
as recommended for cucurbits generally is effective. 

Southern-blight {Sderotium rolfsii Sacc). — A large per- 
centage of the muskmelon and watermelon crops in the 




Fig. 101 . — Muskmelon leaf spotted with downy-mildew. 

Original. 

southernmost states is often destroyed by this disease. It is 
particularly noticeable on fruit upon the side touching the 
ground, first as a slight rot (ground-rot), followed by a white 
fringe of fungous threads which soon surround the whole 
fruit. Later sclerotia appear as small round bodies, dirty 
white to dark brown. For further description and treatment, 
see pepper. 

Angular leaf-spot '^^■'' -^^' ^'^^ (Pseudomonas lachrymans (S. 
& B.). — This disease is now known in many of the eastern 



186 



Diseases of Economic Plants 



and middle states, and causes large loss. Affected fruits rot 
into a soft, slimy, wet mass, this occurring often in transit. 
On the leaves dark, watery spots, 3-5 mm. in diameter, ap- 
pear. The spots later become dry and brown, and the 
brittle tissue usually falls away, leaving a ragged, irregular 

hole. Spots on the 
fruit are at first small, 
2-3 mm., and watery, 
and exude a gummy 
liquid which later dries 
to a white residue. 
Infection proceeds to 
the interior, and in a 
few days the central 
portion becomes a 
rotten mass. Young 
fruits are especially 
susceptible. Care 
should be taken in 
picking to avoid 
wounding the fruit, 
and all affected fruits 
should be most scrupu- 
lously sorted out of 
lots that are for ship- 
ment. The season's 
ing upon a muskmelon at point of con- infection may originate 
tact with the soil. After Hume. ^.^^^^ ^^^^ ^j^^^^^^ 

seed or from soil. The use of seeds treated with mercuric 
chlorid reduces infection. 

Mosaic. "^^' ^^^ — Two mosaic diseases of cucurbits are: 
the White-pickle-mosaic, which affects many hosts, and the 
Mottled-leaf-mosaic, common to only a few hosts. The 
status of knowledge is much as in the case of other mosaics. 
See p. 258. Inoculations are readily made by rubbing. In 
the field, infection is carried by beetles and by the pickers. 
Experiments have shown 18 species in 10 genera of cucurbits 




Fig. 102. — Sclerotium rolfsii Sacc. grow- 



Vegetable and Field Crops 187 

to be susceptible, l^ut the disease is not identical with those of 
bean, tobacco, tomato. Mosaic is regarded as the most 
serious disease of the cucumber in the Middle West, and it 
ranges from California to Virginia and Texas. Mosaic on 
squash and pumpkin appears to be a distinct disease. 

Powdery-mildew ~^^ {Enjsiphe pohjgoni DC). — This mil- 
dew on cucurbits generally has the common characteristics 
of the powdery-mildews, a whitish flourlike coating upon the 
leaves and stems; at first in circular spots, but later diffuse. 
Its presence on cucumbers in America was first announced 
by Humphrey. It has. since frequently been observed in the 
field and occasionally under glass. 

The fungus appears chiefly upon the upper leaf surfaces 
and is most developed upon the older leaves. It renders the 
fruits bitter and distorts them. If it occurs in the greenhouse, 
flowers of sulfur applied to the hot water or steam pipes in the 
form of a paste is useful. 

Stem-end-rot -^^ {Diplodia sp.). — In transit watermelons 
often shrivel and develop a wet, slimy rot, which may progress 
13^ inches in a day. Many cars reach their destination with 
75 to 95 per cent of their contents spoiled. In one day 100 
cars showed an average of 25 per cent loss. Diseased refuse 
should be destroyed, clean culture and deep plowing practiced, 
and cutters in harvesting must avoid spreading the contagion. 
It is recommended that the freshly cut stem-end be coated 
with an antiseptic paste; hot water, 33^ qts., copper sulfate, 
8 oz.; add to starch paste, 4 oz. to 1 pt. of cold water. 

Leaf-blight, fruit-spot "^"^ (Cladosporium cucumerinum E. 
& A.). — This spotting on cucumbers was first noted at 
Geneva, N. Y., in 1887, where it was so abundant as to 
ruin the pickle crop. It is occasional on melons. 

The spots begin, when the fruit is only 2-5 cm. long, as gray, 
slightly sunken areas with delicate, velvety surfaces. They 
are about 3 mm. in diameter, but coalesce into irregular 
patches, particularly toward the flower end. As the spots 
age they darken to greenish black, and a gummy exudate 
often appears. 



188 



Diseases of Economic Plants 



Upon leaves, where injury is less common than upon the 
fruit, the spots are at first watery and translucent; later 
the leaf wilts, and is soon reduced to a decayed mass. The 
disease progresses so fast that a plant may be practically 




y ' " *4#*^ ' 




Fig. 103. — Part of watermelon with stem-end-rot. After Meier. 

destroyed in a few days. Immediate and thorough spray- 
ing may be of service. 

Soft-rot ^^^' ^^^ {Bacillus melonis Gidd.). — This soft-rot 
was described first by Giddings as causing 25 per cent loss of 
muskmelons in certain fields in Vermont in 1907. The decay 
usually begins on the lower side of the fruit, resulting in 



Vegetable and Field Crovs 



189 



shrunken, diseased areas over which the skin remains un- 
broken. The flesh near the point of infection becomes com- 
pletely decayed and has an offensive odor. 




Fig. 104. — Muskmelon 65 hours after inoculation with 
Giddings' germ. After Giddings. 



The cause is a bacillus which gains entrance through 
wounds, often through ruptures occasioned by excessively 
rapid growth. 



190 



Diseases of Economic Plants 



Spraying with Bordeaux mixture is recommended; also 

turning the melons so as to expose all sides to light and air. 

Wilt ^^^ (Mycosphcerella citrullina (Sm.) Gr., Diplodina). — 

This wilt or canker seems to be rare, perhaps affecting to 

serious extent greenhouse-grown 
muskmelons; only occasionally 
field muskmelons and other 
cucurbits. 

Infection is local at the nodes 
in the leaf axil, never at inter- 
nodes. The edges of the infected 
areas are "oily green" in color, 
often with resin-colored, gummy 
exudate. The older parts are 
either dark and gummy, or dry 
and gray, and bear many brown 
pycnidia. 

Spraying with Bordeaux mix- 
ture after the plants are about 
half grown, but before the dis- 
ease appears, and often enough 
thereafter to cover growing 
parts, is recommended. 

Minor diseases 

Leaf-spot (Phyllosticta cucur- 
hitacearumSacc.) on muskmelons 
has been destructive in several 
states, notably so in New Jer- 
sey and Ohio. The spots are 
light-colored and pycnidia ap- 
pear in their centers. 
A Leaf-spot ^^^ {StemphyKum cucurhitacearum Osn.), 3-4 
mm. in diameter, circular or irregular in outline, visible from 
both sides of the leaf, with centers yellow-brown and red 
bordered, is reported from Indiana and Ohio as causing 
some loss. 




Fig. 105. — Portions of musk- 
melon vine showing pycni- 
dia and perithecia of Myco- 
sphaerella. After Dorsey. 



Vegetable and Field Crops 191 

Two Cercospora leaf-spots also occur on cucumber and 
watermelon, and two Septoria leaf-spots on cucurbits gen- 
erally. 

Leaf -glaze ^^^ {Acremonium sp.). — Shoots are stunted, 
fruits deformed, and leaves yellowed and killed. Upon the 
lower leaf surfaces a delicate white, glossy film like dried 
albumen is seen. Plants that are attacked may put forth 
new, vigorous shoots to survive for a time, then die. The 
disease has been known to reduce the yield 90 per cent. No 
treatment has been advocated. 

Blossom-rot (Rhizopus nigricans Ehr., Choanephora cucur- 
bitarurn (B. & Rav.) Thaxt.) spreads to the young squash, 
cucumber, or pumpkin, causing loss of the fruit by soft- 
rot. 

Root-knot (nematodes) . Of the cucurbits, the watermelon 
is very susceptible. Root-rot due to Thielavia is somewhat 
injurious. 

Cucurbit Spraying -"'^ 

Planting should be at such distance as to facilitate ma- 
chine spraying; that is, relatively close in the row, but with 
the rows wider apart than is usual in most sections of the 
country. In cultivating, the vines should be induced to 
spread along the row, and by the use of a vine turner a 
one-foot open alley may be maintained throughout the season 
for the wheels of the sprayer. 

By means of a geared sprayer with proper length of axle 
to cover one row, three rows may be sprayed at one time. 
Particular attention must be given to reaching the under sides 
of the leaves with the spray. Spray first when the vines begin 
to run, using 3-6-50 Bordeaux mixture. For subsequent 
sprayings use 4-4-50 Bordeaux mixture at intervals of about 
ten days if the weather is dry; oftener, if growth is rapid. 
The net profits from this treatment have been as high as 
$163.50 an acre. 



192 Diseases of Economic Plants 

EGGPLANT ^43 

Wilt (Pseudomonas solanacearum) . See tobacco. 

Wilt (Nedria ipomoece Hals.). — Fields have been so 
attacked that scarcely a fruit was gathered. The affected 
plants when half grown take on a yellowish, sickly appear- 
ance, the foliage wilts, the lower part of the stem becomes 
coated with a whitish mold, and the plant usually dies. 
Numerous small, pink perithecia are found upon the stem 
just below, or at the surface of the ground. 

This disease is close kin to the wilt of cotton, and what 
is said in that connection regarding treatment, applies here. 

Another wilt due to a Colletotrichum is reported as the 
cause of large loss in Utah. A similar wilt due to Verticillium 
is also reported. 

Leaf-spot (Phomopsis vexans (Sacc. & Syd.) Hart.). — 
Plants in the hotbed are subject to leaf-spot attack, the 
transplants dying, or it may appear later upon leaves and 
fruit, and result in more or less serious leaf injury. 

Upon the leaf, large, irregular, brown or gray patches are 
produced. Here numerous black pycnidia appear, and later 
the leaf becomes torn. Upon the fruit the spots are at first 
soft and watery, but later become dry and leathery. 

Treatment with Bordeaux mixture or ammoniacal cop- 
per carbonate before transplanting is recommended, fol- 
lowed by similar spraying in the field. Eight sprayings 
with Bordeaux mixture in one test yielded 100 fruits, while 
a similar plat, unsprayed, gave only about half as many. 
Clean culture should be followed. 

Gray-mold (Botrytis fascicularis (Cda.) Sacc). — In this 
rot the purple fruits show tan-colored blotches, followed 
by softening of the tissue and rapid development of a gray 
mold, the fruit in the meantime changing into a completely 
rotten mass. 

Minor diseases 

Anthracnose {Gloeosporium melongence E. & H.). — Pits 
appear upon the fruits, and in these the pink-tinted acervuli. 



Vegetable and Field Crops 193 

Blue-mold {Penicilliwyi sp.) is very similar to blue-mold on 
apples. Damping-ofif (Pythium deharyanum) . — See p. 19. 
Southern-blight (Sclerotium) is common in the South; Cor- 
ticium does some injury to roots and causes occasional fruit 
rot ; Root-knot due to nematodes is common as is also Drop 
{Sclerotinia lihertiana) . 

GARLIC. See onion. 

GINSENG -^-^--^^ 

Blight (Alternaria panax Whet.). — Brown cankers upon 
the stem, and watery spots in the leaf, often involving the 
entire top of the plant, mark this disease. Badly blighted 
plants appear as if drenched with boiling water. It is a 
serious menace to the ginseng industry of New York state. 
The seed crop is sometimes completely lost. 

It can be controlled by thorough spraying with 3-3-50 
Bordeaux mixture as soon as the plants come up, repeated 
every other day during the first few weeks, less often later. 
Diseased refuse should be destroyed. 

Wilt {Fusarium vasinfedum Atk.). — With the first symp- 
tom of attack the leaflets droop, yellow, and die; then the 
entire leaf dies to the base, dries up, and falls off. The 
immature seeds shrivel and fail to mature. Secondary 
decays, soft rots, may follow. 

Methods of control suggested for watermelon wilt apply 
here also. 

Stem anthracnose {Vermiculma dematium (Pers.) Fr.). — 
Numerous black scars appear on the stems a few weeks 
after the plants come above ground. These spread and 
sometimes encircle the stems. The leaflets then brown. 
Often the plants fall over, even before they wilt. The great- 
est loss lies in the destruction of the seed crop. 

Bordeaux mixture applied about three weeks after the 
plants appear in the spring and each three weeks thereafter, 
until August, more often if the season is wet, will control 



194 Diseases of Economic Plants 

the disease. All dead stalks, leaves, etc., should be collected 
and burned in the fall. 

Verticillium wilt {Verticillium albus (Preuss)). — This wilt 
is due to stoppage of the veins by fungous growth, and the 
chief symptom is wilting of the leaves, followed by death of 
the stem and leaves. Sections of the rootstock reveal a 
yellowing of the water ducts and veins, which contrasts 
strongly with the normal white of a healthy plant. 

The disease is largely confined to the older, less vigorous 
roots. It is advisable to remove and dry the infected 
roots and to replace the soil of infested beds with new, 
healthy soil. Soil disinfection should be employed if 
practicable. 

Black-rot {Sclerotinia smilacina Dur.). — Black, warty 
sclerotia upon the root indicate this disease. The roots are 
very black, but upon drying, bleach somewhat. In old age 
this blackening may extend to the center of the root, which 
becomes wet, spongy, and pliable. The disease remains in 
the soil some years after infestation. Sick roots should be 
removed and burned if not marketable. Treat also as 
for wilt. 

Soft-rot. — This rot occurs widely and causes large loss. 
The root decays rapidly, is sticky and ill smelling. The 
leaves turn red and yellow and soon die. A rot ^^^ due to 
Phytophthora cadorum (C. & L.) Schr. is reported as causing 
a loss of 20 per cent in some beds in New York. Damping-off 
(Corticium) is largely prevented by thorough ventilation, and 
the avoidance of excess of moisture in soil and air. Stirring 
the soil to hasten drying, aids. See p. 19. Leaf-anthracnose 
{Pestalozzia funerea, Desm.) is destructive to young plants. 
It appears as a black, velvety growth at the bases of the 
leaves and flower stalks, causing them to die and fall off. 
Spray as for blight. Thielavia-root-rot (Thielavia hasicola) 
is especially harmful to seedlings, resulting in sudden wilting, 
which causes them to bend over and dry up. The fine roots 
are affected as are the roots of tobacco. Dark brown, dry 
lesions are also produced on the roots by a Ramularia. 



Vegetable and Field Crops 195 

Sclerotinia white-rot (Sclerotinia Uhertiana) occurs to some 
extent (see lettuce). Root-knot (nematodes) and Southern 
blight {Sclerotium rolfsii) are also common. 

GOLDENSEAL (Hydrastis) 

Botrytis-blight. This is the most common and widely 
distributed disease of this plant. Ten to 20 per cent of the 
tops are reported affected in New York, Michigan, and 
Wisconsin. 

Blight {Alteniaria sp.). — Spots occur upon the leaves. 
The disease seems to be identical with that of ginseng. 

HOP 

Powdery-mildew (Sphcerotheca humuli (DC.) Burr.). — 
Powdery-mildew, while serious in many parts of Europe, 
has been seen but rarely on the hop in America, and has 
seldom been reported as seriously injurious. It is recognized 
by the usual characters of the powdery-mildews. See grape. 
If it should become troublesome, spraying with Bordeaux 
mixture or ammoniacal copper carbonate must be prac^ 
ticed. 

Leaf-spot {Cylindrosporium humuli E. & E.). — Small, 
rusty brown, angular leaf-spots largely limited by the veins 
are present. They show most clearly upon the lower sides of 
the leaves. Minute black acervuli are present. The disease 
has been reported from several states, but has not been re- 
garded as serious. 

HORSE-RADISH 

Leaf-blight (Septoria armoradce Sacc. and Ascochyta ar- 
moracice FcL). — Ruin is occasionally brought to a crop by 
these diseases. The leaves bear numerous circular spots, 
blanched in the center and pale yellow at their borders. 
Pycnidia are borne in the centers of the spots. Badly affected 
leaves turn yellow and become filled with holes caused by the 
dropping of the dead tissue of the spots. 



196 Diseases of Economic Plants 

Leaf-spots {Ramularia armoradce Fcl. and Cercospora 
armoracice Sacc.)- — These spots are much Hke those of leaf- 
bhght except that no pycnidia are present. 

Black-mold (Macrosporium herculeum E. & M.). — In 
late summer circular, blanched, and later black, moldy leaf- 
spots are prevalent. The injury is not sufficient to warrant 
treatment. 

White-rust {Albugo Candida) and Downy-mildew {Peronos- 
pora) . — These diseases are the same as upon cabbage. 
They are often present but usually insignificant upon horse- 
radish. Root-rot due to Thielavia also occurs. 

KALE and KOHL-RABI. See cabbage. 



LETTUCE 



251 



Drop ^''^ {Sclerotinia libertiana Fcl.). — The outer lower 
leaves wilt, droop, and fall flat upon the ground; a similar fate 
rapidly overtakes the inner leaves, and so on over the whole 
plant, until within a few days the entire plant is dead, lying 
flat upon the ground, appearing much as though scalded by 
hot water. The disease progresses with wonderful rapidity, 
the plants appearing to die in a day. 

Upon the under sides and at the bases of the leaves occur, 
at this time, dense, cotton-like growths of mycelium, and in 
later stages, small, irregular black bodies, the sclerotia, which 
vary from 3-10 mm. long, somewhat less in thickness. The 
sclerotia and the mycelium are unmistakable signs of this 
disease. 

Drop was first definitely recognized in America in 1900, 
though it doubtless did much damage before then. It has 
since then followed the rapidly extending lettuce industry 
into many states and is particularly destructive in the 
South Atlantic seaboard states from Virginia to Florida, 
where its inroads upon the crop grown under cover are es- 
pecially damaging. The causal fungus may persist from 
year to year, as sclerotia, in beds once infested — beds cost- 



Vegetable and Field Crops 197 

ing originally often $1000 per acre — and thus destroy their 
value for lettuce culture. The damage is thus much more 
than injury wrought merely to the current crop. 

The sclerotia, when favorably situated, are capable of 
germination, each producing several trumpet-shaped organs 
(Fig. 106), with stems about 15 mm. long and disks 3-8 mm. 
or less in diameter. Spores, capable of initiating the fungous 
growth upon dead or sick lettuce tissue, issue in great num- 
bers from these disks, and from material thus infested the 
fungus can make its way into the healthy lettuce plant. 




Fig. 106. — Sclerotia of Sclerotinia from lettuce germinating. 

If all infected plants be pulled and burned as soon as the 
first indication of disease is observed, the formation of 
sclerotia will be prevented. As an additional precaution 
it is well to spray the areas occupied by diseased plants 
thoroughly with Bordeaux mixture or bluestone solution. 

A few years of such procedure will much reduce the in- 
fection or perhaps eliminate it entirely. All lettuce trash 
should be removed from the beds, since it serves as the ini- 
tial point of attack for the fungus. Growers whose land is 
free from the disease should guard against its introduction 



198 Diseases of Economic Plants 

upon diseased refuse in any form. Compost which may be 
contaminated with lettuce refuse bearing this disease should 
be avoided. Those growing lettuce under glass have found 
soil disinfection effective and practicable. 

Damping-off. See p. 19. 

Gray-mold {Botrytis cinerea Pers.). — Gray-mold is es- 
sentially a leaf disease, beginning usually at the leaf edges, 
and there causing wilted, flaccid patches which soon become 
coated with a straw-colored downy fuzz, the sporiferous 
hyphse. The whole leaf, ordinarily an outer one, may droop 
and die. 

Weak plants may succumb entirely to such attack, the 
disease passing slowly from the outer to the inner leaves. 
In all cases after the death of the affected parts a charac- 
teristic, brownish, fuzzy coating appears. This disease may 
be distinguished from drop by the absence of the white 
mycelium and sclerotia, and by the presence of the gray 
Botrytis growth, which is not a feature of drop. The two 
diseases, while often occurring separate, may both infest the 
same beds or the same plants. Gray-mold may also cause 
damping-off. 

High temperature, lack of ventilation, and lack of vigor in 
the plant, resulting from improper care, are conditions favora- 
ble to attack of gray-mold. Precaution with respect to 
these details is sufficient to insure against serious loss. 

Rosette {Corticium vagum). — A moist rot sets in, first 
upon portions of leaves which touch the ground, and spreads 
thence throughout the leaves, rotting away the blades but 
leaving the midribs standing, thus distinguishing this from 
all other diseases. Infection proceeds from leaf to leaf at 
point of contact, often reaching the center of the head, 
while the outer leaves are infected only in spots. The inner 
leaves may all be reduced to a slimy mass though the outer 
leaves still remain, surrounding it as a rosette. 

Downy-mildew (Bremia laducm Regel) . — This occa- 
sionally destructive mildew shows the character of the 
downy mildews, i. e., downy fuzz below, yellow spots above 



Vegetable and Field Crops 199 

(see grape) . It is frequently reported as causing much loss to 
lettuce under glass, especially upon the older leaves. It is 
also noted upon old leaves on seed plants of both cultivated 
and wild lettuce. 

Close attention to proper cultural conditions in the green- 
house, especially as to moisture, ventilation, and tempera- 
ture, usually suffice to hold it in check. Evaporated sulfur 
also aids in suppressing the mildew. 

Bacterial rots -^^ {Pseudomonas sps.). — Several different 
rots due to bacteria occur upon this host. In some instances 
the head rots at the center, or at the top. In other cases 
leaves may become spotted with large brown or black areas, 
or shriveled, or give way to a soft rot, or the tips of the heart 
leaves may die. In other instances, small translucent leaf 
spots occur; extending and coalescing, they occupy large 
areas, the affected tissues becoming dry and papery. 

Various species of Pseudomonas, associated with these rots 
have been considered causal agents, but predisposing condi- 
tions, as extreme cold, or other unfavorable conditions of 
temperature, ventilation, or nutriment seem to be necessary 
to enable these bacteria to gain entrance into the plant. 

Leaf-perforation, anthracnose ^^^ {Marssonina panat- 
toniana (Berl.) Magn.). ^ — ^The most conspicuous character 
is perforation resulting from the fall of the tissue killed by 
the attacking fungus. These perforations are from 1-2 mm., 
or more, in diameter, with irregular borders. Upon the 
midrib and petiole depressed spots result. With small, 
young leaves dwarfing and distortion is produced, especially 
at the apex. The disease appears to be limited to green- 
houses and to be spread largely by watering. 

It was first described by Selby in Ohio in 1896 and has 
since been noted in several other states, ranging from the 
Atlantic to the Pacific, and in Europe. Diseased lettuce 
should be burned. Watering by overhead systems leads to a 
minimum of infection. 

Blight {Septoria laducce Pass, and Septoria consimilis E. & 
M.). — Upon the old, outer head-leaves there often appear 



200 Diseases of Economic Plants 

numerous, black pycnidia, so small as to remain unnoticed 
unless by special search. The injury is usually insignificant, 
though some dwarfing and curling of the leaf results. Upon 
seed plants these same diseases attack the leaves with 
greater vigor, causing pale brown, discolored areas and 
the death of the older leaves. Sometimes, through neglect 
to destroy plants of the seed bed, these diseases may gain 
such foothold as to cause injury in other beds. This can 
usually be avoided by destruction of the seed-bed plants as 
soon as transplanting is over. 

Root-knot (nematodes) occurs on lettuce, doing some 
damage. 

MANGOLD and MANGEL WURZEL. See beet. 
MELON. See cucumber. 

MUSHROOM 

Mold -^^ (Mycogone pernidosa Magn.). — Though noted 
in Germany as early as 1887 this disease was not called to 
attention in America until 1909. 

French experts detect the disease first in the spawn as 
an abnormal, white, fluffy growth. Later the mycelium of 
the mushroom fails to develop normally, but instead pro- 
duces monstrous soft growths. Whole clumps develop 
into moldy masses, which soon putrify with a disagreeable 
odor. 

Infested beds or houses may be abandoned or cleaned 
thoroughly, then fumigated with formalin, 3 pints, per 1000 
cubic feet of space. 

Bacterial-spotting.^''^ Small areas, pale yellow to brown, 
on cap, stipe, or gills, or even covering the whole plant, 
occur. Fumigating the beds with sulfur before planting has 
given excellent results. 

MUSKMELON. See cucumber. 



Vegetable and Field Crops 201 



OKRA 



Wilts -^^ {Fusarium vasinfeduin Atk., Vertidllium alho- 
atrum R. & B.). — Two wilts of okra, macroscopically in- 
distinguishable from each other, occur; both partake of the 
general character of wilts discussed elsewhere, pp. 26, 253. 

Pod-spot {Ascochyta abelmoschi Hart.) is reported from 
New York and Maryland, and a Leaf -spot (Cercospora) from 
Porto Rico. Texas-root-rot (Ozonium) is injurious in the 
Gulf states. 

ONION, GARLIC, CHIVE ^^'^ 

Smut 255-257 (^ Urocystis cepulce Frost) . — As with the wilt of 
tobacco and cotton, this fungus resides in the soil and is 
therefore destructive not only to the present crop, but is 
also prohibitive of successful culture of susceptible crops 
in the future. 

The smut, which seems to have originated upon a wild 
variety of onion, occurs in both Europe and America. It 
was known in Connecticut as early as 1860, Massachusetts, 
Pennsylvania, and Ohio in 1889, later in New York, New 
Jersey, and Delaware, and has since been recorded from 
Iowa and Georgia. The first mention of serious loss by 
onion smut in America was in 1870. Its inroads upon the 
crop are often such as to prohibit profitable onion culture 
unless preventive measures are taken against the disease. 

The smut attacks the very young seedlings through the 
still tender, delicate leaf sheaths. Onions' grown from 
sets are immune, and onions from seed, if they pass the 
very young state without infection, are so protected by 
hardening of the outer plant parts as to resist attack, even 
if the bulb is surrounded by thoroughly infested soil. 

Upon the infected seedling leaves, dark, opaque spots 
may be noted, especially upon holding the leaves against 
the light. The portions of the leaf above such spots soon 
die, and the spots rupture, exposing sooty, powdery masses. 
Badly infected seedlings succumb early, while others may sur- 



202 



Diseases of Economic Plants 



vive until harvest. The disease is more often fatal if attended 
by dry weather, which reduces the vigor of the host plant. 




Fig. 107. — Young onion plants showing effect of smut. 
At left, smutted plants; at right, healthy plants of 
the same age. After Hinman. 

Plants surviving the disease show smut in the outer leaves, 
often also within. Diseased bulbs dry up and rot. In han- 
dling they may readily be distinguished from sound bulbs. 
The spores are liberated freely in the soil, where they 



Vegetable and Field Crops 203 

may remain alive for many years. The disease may be car- 
ried to adjacent fields by insects, also by the means sug- 
gested under soil diseases. There is little or no danger of 
disease carriage by the seed. 

Since onion sets are immune, the effects of the smut can 
be avoided by sowing seed in soil that is free of disease and 
then transplanting into the field. With this mode of onion 
culture the only difficulty is to secure plats free from in- 
festation, and this is not often a serious one. In extreme 
cases disinfection of the soil in plats may be resorted to. 
(See soil disinfection, p. 460.) On farms once infested all 
refuse (screenings, tops of infected sets) should be collected 
and burned to reduce the amount of spores. Where soil, 
known to be infested, is to be planted, formalin (1 ounce in 
1 gallon of water) should be used and applied with a drip 
attachment on a seed drill in the proportion of one gallon 
of solution for each 1200 linear feet of row. 

Ground quicklime or stone lime, better the former, ap- 
plied at the rate of 75 to 125 bushels per acre on the freshly 
prepared soil just before seeding, has been useful. If ap- 
plied by drill, harrowing will not be required; if broadcast, 
harrowing should precede planting. One hundred pounds of 
sulfur mixed with fifty pounds of air-slaked lime applied in 
the drills is also effective. 

These methods used separately or combined are suffi- 
ciently established to warrant general use on smutted soils 
devoted to onion culture. 

Downy-mildew, -^^' ~''^ blight (Pero?iospora schleideni Ung.). 
— Close kin to the disastrous blight of potatoes, this disease 
partakes of many of its characters, particularly in the rapidity 
of its spread through an infested field. It may first be noted 
on a small area of the field in which the tips appear as though 
dashed with scalding water. Often under favorable climatic 
conditions the affected areas increase many fold in a single 
night, carrying complete destruction. 

It was first described in 1841 by Berkeley as ''common 
and destructive," and has long been known to onion growers 



204 



Diseases of Economic Plants 



in this country, in Europe, and in Bermuda. In the latter 
place it was so injurious that the legislature applied to the 

mother country for investigation and 
aid. The first reference to it in the 
United States was in 1872. It is now 
reported from coast to coast. 

The blight was described fully by 
Thaxter in 1889, again by Whetzel in 
1904, during which latter year it was 
particularly destructive in New York, 
causing a loss of half the yield, even 
more in some instances. 

The attack in the field occurs first 
upon a few plants during warm, damp 
weather. Examined while the dew is 
still present, these plants, seen from 
considerable distance, display a peculiar 
violet tint especially easy to discern 
through the dewy covering. Close ex- 
amination shows the affected part to 
be covered with a fuzzy coating. On 
the second day these parts lose their 
green color, turn pale, or even yellow. 
On the third or fourth day the plant is 
entirely collapsed. 

The diseased spots in the field may 
each cover an area of only a few feet in 
diameter, enlarging slowly. If the 
weather favors the fungus, the disease 
may sweep rapidly across the whole 
field. Affected plants, under suitable 
weather conditions, brilliant, dry atmo- 
sphere, recover slowly, putting out 
new leaves. Subsequent attacks may occur if the weather 
favors the growth of the fungus. The injury from 
this disease is through the loss of leaf surface, thus re- 
ducing the growing power of the plant. Usually little or 




Fig. 108. — Onion 
plant illustrating 
manner of death 
of leaves affected 
with downy-mil- 
dew. After Whet- 
zel. 



Vegetable and Field Crops 205 

no increase in the size of the bulb occurs after a severe 
attack. 

To prevent the spread of the disease, and to lessen the 
danger from subsequent attacks, a spray of Bordeaux mix- 
ture, 5-5-50, should be apphed as soon as the disease is 
noticed. Careful supervision and spraying to check re- 
newed attacks of the fungus, particularly if the weather 
continues to favor its development, should not be neglected. 
New growth should also be protected by the use of Bor- 
deaux mixture. 

Infection in previous years warrants spraying before 
the disease appears; also throughout the season, reaching all 
sides of the leaf with the fine spray and using high pressure 
to make the mixture adhere to the smooth onion leaves. 
Wet lands are more subject to this disease and should be 
avoided if possible. It is recommended to rake and burn 
the dead tops, to destroy the infective spores within them, 
and to practice crop rotation. 

Black-spot ^^^ (Cleistothecopsis circinans, S. & T., Volu- 
tella, also known as Vermicularia and Colletotrichum) . — 
The outer scales of the bulb after harvest often show 
black growths of pecuHar and striking character. They con- 
sist of central, black dots or very small rings, around which 
from one to several larger rings are arranged concentrically. 
Under moist conditions these markings enlarge rapidly by 
the production of more rings or wavy lines, or, under some 
circumstances, the whole area may be overgrown with black. 
Later the disease may extend through the outer bulb scale 
and into the next and succeeding layers to considerable 
depth, causing rot. 

While the disease is not conspicuous before harvest, it is 
really present in the incipient stage upon the bulbs in the 
field and continues to develop rapidly under storage con- 
ditions. Here it may pass to new bulbs by contact or by 
air currents. These dangers are much augmented by a 
moist atmosphere. While the growth is not retarded ap- 
preciably by this disease, the value of the onion is often 



206 



Diseases of Economic Plants 



much reduced by the disfiguring spot, and the loss from rot 
induced by it is also considerable. 

Onions before they are placed in storage should be well 
dried. Storage bins with good ventilation, so arranged 
as to prevent all heating or sweating of the bulbs, should 
be provided. No infected bulbs should be stored, since 
they will carry infection to the sound bulbs. Bins that 




Fig. 109. — Black-spot on onion. Original. 



are known to be infested, i. e., which held infected onions 
in any preceding year, should be disinfected by a thorough 
spraying with Bordeaux mixture or plain bluestone solu- 
tion. The white varieties of onions are much less resistant 
than the red and yellow kinds. 

Neck-rot -^^ (Botrytis allii Munn). — This rot is generally 
distributed in onion sections of the United States and Europe, 
and causes heavy losses to stored onions as well as to crops in 



Vegetable and Field Crops 207 

the field. The neck of the onion, where the top has been cut 
off, is coated with a fuzzy, pale brown or gray mold, and later 




Fig. 110. — Black-spot showing variation. Original. 

this area bears few or many black sclerotia. The mold oc- 
curs also in water-soaked spots on leaves and seed heads. 

Diseased bulbs should never be set out. All diseased refuse 
should be destroyed. The crop must be thoroughly cured 
and dry before storage. 



208 



Diseases of Economic Plants 



Soft-rot ^^^ (Bacillus carotovorus). — This soft-rot, first 
noted in New York in 1898, is a common cause of loss of 
onions. In many fields, one-third to one-half of the crop is 




Fig. 111. — Botrytis sclerotia at necks of bulbs. 
After Munn. 



destroyed, and the balance of the crop injured by the pres- 
ence of the rot. 

Frequently a single leaf scale of an otherwise sound onion 
is entirely rotten, or again several scales may be rotted. If 
the outer scale is rotted, the bulbs are designated by the 
growers as ''slippery onions." The rot does not spread from 



Vegetable and Field Crops 



209 




Fig. 112. — Onions affected with soft-rot; longitudinal and cross sec- 
tion. After Stewart. 




Fig. 113, — Black-mold due to Sterigmatocystis. Original. 



210 Diseases of Economic Plants 

scale to scale within the bulb. In dry onions in storage its 
progress is slow, but wet onions decay rapidly. The only 
suggestion toward control is to keep onions dry in storage. 

Minor diseases 

Black-mold (Macrosporium yarasiticum Thiim. and M. 
porri Ell.). — Frequently onion leaves that have been in- 
jured assume a velvety, black coating, which often appears in 
spots, or covers them entirely. Treatment against other 
diseases, and maintenance of the plants in full vigor is of 
most service in this case. Another cause of black-mold ^^^ is 
Sterigrnatocystis nigra v. Tiegh. It most commonly appears 
forming dark masses of spores, resembling a smut, under the 
outer scales of the bulb. In this form, the injury is due only 
to unsightliness. Frequently, however, the fungus grows 
into the lower scales of the onion, causing a slimy, soft rot. 
It is not essentially a field disease, but one of chief importance 
during storage. Sanitary measures to prevent the develop- 
ment of the mold on refuse in the field are advised. Infested 
sacks, crates, bins, etc., should be disinfected. Pink-root ^^^ 
(Fusarium malli Taub.). — The affected roots turn yel- 
low, later pink, then dry up. New roots that develop 
also become diseased. The bulbs are dwarfed. The loss 
sometimes is as great as 40 per cent of the crop. The 
infection comes from the soil, and the general remarks 
under soil diseases (p. 26) apply here. Two rusts occur, 
Pucdnia porri (Sow.) Wint. on the chive, P. allii DC. on 
onions. 

PARSLEY. See celery. 
PARSNIP. See celery. 

PEA 

Spot '^^^ {Mycosphcerella pinodes Berk & Blox., Asco- 
chyta) . — Spotting of pea leaves and pods has been known to 



Vegetable and Field Crops 



211 



farmers for many years. It is most conspicuous upon the pods 
as circular, somewhat sunken spots, 3-6 mm. in diameter, 
which are dark bordered, pale in the centers, or, when ma- 




FiG. 114. — Pea leaves showing the spot disease. After van Hook. 



ture, somewhat pink. In these spots numerous pycnidia are 
visible and under favorable conditions the spore masses 
issuing from them may be seen with the naked eye. Upon 



212 



Diseases of Economic Plants 



the leaves, similar oval spots, 3-10 mm. in diameter, with 
the pycnidia usually in concentric circles, are abundant. 
The lower, older leaves are affected first, resulting in their 

death. The younger leaves die 
later. Stems are subject to the 
same attack — first near the 
ground, later upon all parts; the 
spots often penetrating through 
the woody part, thus causing 
wilting and death of the parts 
beyond. The stem attack is the 
most serious form, since it di- 
rectly causes death to a large 
part of the plant. This is espe- 
cially true if the disease be fol- 
lowed by dry weather. 

All forms of the disease tend to 
decrease the yield in proportion 
to their prevalence. Plants not 
killed before flowering may de- 
velop pods, though of lessened 
yield. 

Disease upon the pod may 
^^ penetrate completely through it 

^toHHpr M^ and appear upon the opposite 

^^^ side, or more frequently it may 

grow into the seed within the 
pod. Seeds badly diseased in 
this manner adhere to the pod; 
if less affected, they thresh out, 
are shrunken, and show, according to the color of the 
variety, more or less discolored spots. Often seeds are 
diseased, and yet so slightly disfigured as to escape ob- 
servation. 

Trial has demonstrated that of badly infested seeds only 
6 per cent are capable of germination, and that even when 
they do germinate, the resulting plants seldom reach ma- 




FiG. 115. — Spotted pods of 
French June field pea. 
After van Hook. 



Vegetable and Field Crops 213 

turity. On young plants the disease often assumes the 
character of damping-off. 

Aside from the pea this disease attacks alfalfa, bean, and 
hairy vetch. It was a grave menace in Europe in 1894, in 
Canada in 1903, in Ohio in 1904. In New York, in 1906, from 
50 to 80 per cent of the crop was injured. 

Two years' rotation in nonsusceptible crops lessens the 
evil. Diseased seed should be avoided. 

Bacterial-blight -^'' {Pseudoinonas pisi Sack.). — The stems 
are discolored, watery, olive-green to olive-brown; the leaflets 
and stipules appear bruised and yellow. The disease is 
known in Colorado, Nebraska, Dakota, and Utah, and in 
severe outbreaks has been known to kill 30 per cent of 
the plants. 

Wilt {Fusarium sps.). — Two wilts, both due to Fusarium, 
have been described. They agree essentially with the de- 
scription under cowpea. 

Minor diseases 

Powdery -mildew {Erysiphe polygotii DC.) develops most 
conspicuously late in the season, and sometimes becomes so 
injurious that the plants do not mature seed. Though it is 
not usually very destructive, 20 per cent injury has been 
reported from Ohio; 33 j^er cent from some parts of Nebraska. 
The fungus hibernates in seed derived from affected pods. 
Such seed should not be used for planting. Liver of sulfur or 
Bordeaux mixture is effective in the field. 

Black-mold (Pleospora pisi (Sow.) FcL). — Frequently 
moldy, black spots are noted upon pea pods, leaves, or other 
parts. This condition is chiefly a secondary disease following 
some other injury. 

Stem-rot {Cortidum vagum) is somewhat injurious, as is 
also the Root-rot (Thielavia), and Root-knot (nematodes). 

Damping-off. See p. 19. 

Rust is rare on pea. See bean. 



214 Diseases of Economic Plants 

PEANUT 

Leaf-spot (Cercospora personata (B. & C.) Ell.). — This 
leaf -spot is circular in outline, indefinitely bordered, black 
to brown in the center and grading to green on its outer 
edge. The lower leaves are first affected and suffer most; 
later the disease spreads to the upper leaves. The leaves 




Fig. 116. — Peanut leaf-spot. After Wolf. 

begin to fall soon after they spot, and in many cases the 
death of the plant results. It is often a pest. The causal 
fungus was first collected in Carolina and Alabama by 
Ravenel. 

Southern-blight {Sclerotium rolfsii) does some damage. 
(See pp. 23, 215.) The true rust {Uredo arachidis Lag.) is 
injurious in the sub-tropics. Red-rot of the pods, charac- 
terized by brown discoloration and the presence of red 
perithecia {Neocosmospora) is of slight importance. 



Vegetable and Field Crops 



215 



PEPPER 

Southern-blight, wilt ^^ {Sclerotium rolfsii Sacc). — Blight 
shows itself first by a slight drooping of the leaf tips by day, 




Fig. 117. — Pepper plant showing effects of the 
Southern-blight. After Fulton. 



followed by night recovery. The wilt becomes more pro- 
nounced on succeeding days until in the third or fourth day 
the leaves wilt permanently, lose color, dry, and soon fall. 
These stages may succeed each other so rapidly as to ap- 
pear almost simultaneous. The roots appear normal; but 
on the stem near the ground are found shrunken, dis- 



216 



Diseases of Economic Plants 



colored areas in the bark, often extending part of the way 
around the stem. Later the roots may rot from secondary 
causes. 

Upon the diseased spots are fine myceUal strands, espe- 
cially abundant under humid conditions. Soon these strands 

unite into tufts, which 
round off, become hard 
and smooth, and 
change from white to 
yellow, and finally to 
dark brown. These 
bodies, the sclerotia, 
are about as large as 
mustard seeds. At- 
tacks usually begin 
when the pods are 
forming and continue 
throughout the season. 
This disease has been 
found in many South- 
ern states upon a wide 
range of plants. See 
p. 23. 

The application of a 
clear, preventive fun- 
gicide, such as ammo- 
niacal copper carbon- 
ate, to the ground at 
the base of the plant, and where any part touches the 
ground, so that it can soak into the ground near by and 
cover the stem itself, has proved beneficial. The first ap- 
plication should be made at the earliest sign of blight, or 
still better, in anticipation of it, and should be followed by 
other applications at intervals of two to three weeks. Bor- 
deaux mixture is not suitable, since the effective material is 
filtered out by the soil. 

Black-mold (Macrosporium sp.). — This malady renders 




Fig. 118. — Pepper plant showing fun- 
gus of Southern-blight. After Fulton. 



Vegetable and Field Crops 217 

the fruit moldy and black, particularly at the blossom end. 
It is one of the most destructive of pepper diseases. 

Minor diseases 

Anthracnose {Glomerella piperata (E. & E.) S. & S., Gloeo- 
sporium). — Soft, circular, pale, sunken spots upon the fruit 
accompanied by small, ruptured spots in the skin, through 
which the pink spore masses protrude, indicate this disease. 
Anthracnose due to Colletotrichum nigrum E. & H. is of 
similar appearance except that the centers of the soft spots 
change to a decided black as they age. Mosaic similar to 
that of tobacco is often present. Black-spot, caused by 
Alternaria entering through wounds due to sun-scald or 
frost, sometimes injures 45 per cent of the fruits. A Fruit- 
rot is caused by Sclerotiurn bataticola Taub. Leaf-spot 
(Phyllosticta sp.) shows small, circular spots of ashen color, 
bearing pycnidia. Other diseases are: Leaf-spot (Cercos- 
pora capsici H. & W.), Soft-rot (bacteria), Root-knot 
(nematodes) . 

POTATO 

Late-blight -^^-"'^^' ^^^~ {Phytophthora infestans (Mont.) De 
Bary). — In the year 1889 Lamson-Scribner, writing of 
this, the most serious potato disease, said, ''It prevails in all 
potato countries of the world, and causes more damage to the 
potato than all other injuries combined." It is possible that 
all that he regarded as blight would not to-day be included 
under late-blight; still the disease holds its place as one of 
the most destructive plant diseases of the world. 

It is estimated that in New York state alone the blight 
caused a loss of $10,000,000 in 1912, and the total loss in the 
United States in 1917 is placed at 24,000,000 bushels. The 
loss reported in one year from Ohio was $2,000,000; from 
Wisconsin $5,000,000. The blight is supposed to have 
originated in South America and to have been brought to 
this country about 1840. 

The disease may appear on any part of the leaf, but the 



218 



Diseases of Economic Plants 



spots generally show first near the tip or margin, probably 
because surface water remains longer on these parts. The 
diseased area soon blackens and dies. The diseased part may 
temporarily dry out and curl up if the progress of the fungus 
is checked by drought, or the blight may, in rainy weather, 
rapidly proceed to transform the entire fohage into a moist, 




Fig. 119. — Potato late-blight. Rows at left sprayed with Bordeaux 
mixture and Paris green; rows at right received Paris green only. 
Original. 



putrid mass. In the earlier stage the blackened part is 
bordered by a narrow region of light green, characterized 
by a slightly watery, flaccid appearance. Under conditions 
of especially humid atmosphere a fine, white down may be 
seen upon the more recently invaded parts. This affection 
of the leaves is accompanied by an offensive odor discernible 
at considerable distance from the field. The disease usually 
soon shows on the stems also, which in turn blacken and die. 



Vegetable and Field Crops 219 

On the surface of the tuber shghtly depressed, dark- 
colored areas appear while internally the normal white color 
changes to dirty brown. If the soil is dry, dry rot results; 
if wet, the tubers decay as wet, slimy, ill-smelling masses. 
In storage the disease continues, and the loss sustained in 
the field may be greatly augmented. 

This blight is closely dependent upon conditions of heat 
and moisture. A daily mean of 22° to 23° C. (72°-74° F.) 
accompanied by moist weather conduces to its spread. A 
daily mean temperature above 25° C (77° F.) for a few days 
retards its development. 

Although the conspicuous signs above noted first attract 
the attention of the general observer, the disease really 
commences as soon as the sprouts appear. Young plants 
grown from infected seed remain dwarfed, assume a reddish 
brown color, and when proper weather conditions obtain, 
furnish the spores to start the general attack. 

Marked difference in resistance exists among varieties. 
Thus in Maine the Rust-proof showed the highest resistance, 
about 1 per cent of disease, while no other varieties tried gave 
less than 30 per cent of disease. Of the standard crop vari- 
eties the following are reputed to possess some degree of 
resistance: Carmen No. 3, Sir Walter Raleigh, Rural New 
Yorker No. 2, Rural Blush, Green Mountain, State of Maine, 
Delaware, Enormous, and White Beauty. 

Field trials have shown that certain German and English 
varieties are more highly resistant than the American vari- 
eties. It is a hopeful sign, therefore, that American potato 
breeders are now giving attention to disease resistance and 
that new varieties of greater excellence in this respect may 
be expected in the future. 

Healthy potatoes only should be used for seed. Diseased 
potatoes may be recognized by their reddish brown surface 
color, which extends toward the center of the potato; also 
by the slight shrinking of the surface in such parts, or by the 
spotting described above. 

The crop should be sprayed as recommended under the 



220 



Diseases of Econo?nic Plants 




general heading, p. 236. Though the disease may not develop 
annually in severe form, spraying is necessar}^ each year as a 
preventive measure. Since the blight develops rapidly, it is 
quite impracticable to wait for signs of the disease before 
spraying is begun. Moreover, experiments extending over 
several years have shown that even in years when the blight 

does not become epidemic, sufficient 
benefit is derived from spraying to 
warrant its adoption. 

The Geneva Experiment Station 
says: '^ Judging from the experiments 
thus far made, it appears that spray- 
ing for l3light is an operation which no 
potato grower in New York can afford 
to neglect. Forty-eight farmers' busi- 
ness experiments show an average 
net profit of $20.51 per acre due to 
spraying." 

Commence spraying with Bordeaux 
mixture when plants are 6 to 8 inches 
high and repeat at intervals of ten to 
fourteen days throughout the season, 
making, in all, five or six applications. 
AVhen Inigs or flea beetles are numerous, add Paris green or 
other poison. In case the tops have blighted, the danger of 
tuber infection and consequent rot is lessened by delaying 
the harvest of the tubers until at least a week or ten days 
after the death of the foliage. 

Common-scab -'2-274 {Actinomyccf^ scabies (Thaxt.) Giiss.) — 
Scab prevails in Europe, Africa, New Zealand, in all parts of 
the United States, and probably wherever the potato is 
grown. It was first attributed to its proper cause by Thaxter 
in 1890. 

Common-scab is recognized by all potato growers as a char- 
acteristic, rough pitting of the tubers. If potatoes are at- 
tacked when quite yoimg, the scabs are deep; if the attack is 
later, they are more shallow. In severe cases the tuber is 



Fig. 120. — Common 
scab produced by 
inoculation forming 
monogram R. T. 
After Thaxter. 



Vegetable and Field Crops 



221 



furrowed or cracked. Mites often follow scab, making the 
pits much deeper. 

The scab at first appears as a minute reddish or brownish 
surface spot, often when the potato is very young. It ex- 
tends outward, deepens in color, and is attended with the 
development of an irregular, corky incrustation. 

The disease is often prevalent to such an extent as to pro- 
hibit successful potato culture. The chief loss comes from de- 
preciation in sale value, though there is also loss in yield. 




Fig. 121. — ^ Potato common-scab. iVfter Melhus. 



Estimates show that from 5 to 75 per cent of the potato crop 
is unsalable on account of scab. The loss in California in one 
county alone is placed at $300,000 yearly. 

Common-scab is most prevalent in alkaline soils and is 
favored by moisture. Wood ashes, potash, soda, stable 
manure, lime, etc., increasing alkalinity, favor the growth 
of the fungus, and cause increase in the amount of scab in 
soil already infested. Materials which tend to decrease scab 
are commercial fertilizers, potash salts (except carbonate), 
land plaster, and ammonium sulfate. Rotation of crops tends 



222 Diseases of Economic Plants 

to diminish the amount of scab, provided other susceptible 
crops, as beets, turnips, cabbages, etc., are avoided. A 
three-year rotation without a susceptible crop largely re- 
duces it, though after five or even ten years the fungus 
may not be entirely exterminated. During rotation any 
practice that increases the acidity of the soil aids in reduc- 
ing scab. Thus plowing under green crops is a favorable 
practice. 

In general it may be said that scabby seed potatoes in any 
soil will produce a scabby crop, but the amount of scab is 
determined somewhat by the conditions. Seed potatoes free 
from scab, in a soil free from scab, will raise a crop free from 
scab. Seed potatoes free from scab will not produce a healthy 
crop if grown in infested soil; but less scab will result than 
when diseased seed is used. 

There is much difference in varietal resistance to scab. 
The more resistant varieties should be used on infested 
soil. 

Two conditions arise requiring different cultural meth- 
ods: — 

1. The management of clean soils. 

2. The management of soils already infested. 

If the land is free from infestation, great care should be 
exercised to avoid introduction of the scab fungus by any of 
the general means suggested under soil disease, p. 26. In 
particular, infestation may occur by the use of scabby seed, or 
through the use of manure which has been infested by feed- 
ing uncooked, scabby potatoes to stock. If seed must be 
planted that cannot safely be regarded as free from scab, 
and no seed from an unknown source can be so regarded, it 
should be disinfected to free it of scab germs. See p. 240. 

No system of soil treatment has proved reliable in the 
management of infested land. Long rotation, avoiding 
susceptible root crops, should be' practiced. The use of 
fertiHzing materials which favor the fungus should be avoided 
and resistant varieties should be planted. The turning 
under of a green crop, e. g., rye, may gradually decrease the 




IiG. 122. — Potato l)adly infested with wart. After Kunkel. 



224 



Diseases of Economic Plants 



scab tendency. The benefit of treating seed to be used on 
infested soil varies largely with local conditions. 

Wart "''^' ^^^' ^"^^ (Synchytriuni endobioticum (Schil.) Perc, also 
known as Chrysophlyctis) . — This disease invaded America 
(Newfoundland) about 1909, and recently was (Sept., 1918) 
found in several counties of Pennsylvania; still more recently 
in Virginia and West Virginia. It has long been known in 




Fig. 123. — Potato infested with powdery- 
scab. After Melhus. 



England and Europe. Badly diseased potatoes are entirely 
replaced by a white, warty mass; in milder cases, only a few 
eyes are affected with either brown or black spots, or with 
dark warts of size varying from that of a pinhead, upward. 
Soil once infested must not be used for potatoes, neither 
may diseased seed be used. Great care should be exercised 
to prevent wider distribution of this dangerous disease in 
America. 

Powdery-scab ^"^^ {Spongospora suhterranea (Wallr.) Johns.) . 
— Known in Europe since 1841, this disease was first re- 
ported in the United States in 1913, probably having been 



Vegetable and Field Crops 225 

introduced through foreign shipment in 1911. It is now 
prevalent in certain parts of Canada and in Maine, Massachu- 
setts, Nebraska, New York, Washington, Oregon, and 
Minnesota. The tubers are infected when very young. At 
maturity the infected area becomes a pit, filled with dusty, 
yellow spore-balls; the pit bordered by remnants of the 
tuber's skin. The sale value of the potato is decreased, the 
yield lessened, and its value for seed purposes lost. 

Precautions should be taken to guard against infected 
seed. 

Black-scurf -^•^' ^^^' ^^^ {Corticium vagum B. & C, Rhizoc- 
tonia). — Though particularly prevalent in the Middle West 
and Rocky Mountain states, this pest is also known generally 
in the East, from Connecticut southward. Infected tubers 
are largely responsible for the contamination of new soil. 
They may be recognized by the superficial, irregularly 
shaped, scurfy, dark-brown patches (sclerotia) of fungous 
threads varying in size from a pinhead to a grain of wheat. 
They are seen clearly only when the tuber is wet. 

Soon after planting the young sprouts are attacked by 
this waiting fungus. Black spots appear near the surface of 
the ground, destroying the bark and often girdling the stem. 
In such cases aerial tubers often form, and the plants are 
malformed and stunted. A dark network of fungous threads 
is sometimes seen upon the subterranean parts. The fungus 
advances above ground and develops a gray spore-bearing 
layer about the green stem, often extending upward several 
centimeters, causing the young shoots to wilt, droop, and die. 
Often a loss of one-fourth to one-third of the plants follows. 
Stems that survive this early attack, but succumb to later 
attack, produce only a few underground tubers, small and 
unsalable. 

Stem lesions similar to those of black-scurf are also pro- 
duced by a number of different fungi. 

Only clean seed should be used. If there is any doubt, it 
should be treated as is recommended for potato common- 
scab, but even this treatment is not effective if large sclerotia 



226 



Diseases of Economic Plants 



are present on the seed. Liming the soil, clean culture 
methods, and crop rotation are palliative. Infested refuse 

should be destroyed 
by fire. Soil badly 
infested should not 
be planted to pota- 
toes. In general, the 
remarks made under 
soil diseases apply 
here. 

While this disease 
has long been recog- 
nized in Europe, 
especially in Ger- 
many, no record of it 
was made in America 
until 1891. Since 
that date it has been 
noted upon many 
hosts in many states. 
Seep. 21. 

Early-blight 279 (A?- 
ternaria solani (E. & 
M.) J.&G.).— This 
is one of the very 
serious potato dis- 
eases. In 1906 the 
loss in Wisconsin was 
placed at about 
5,000,000 bushels, 
and a 50 per cent loss 
was reported from 
Wyoming. The average loss in Michigan is estimated as 25 
per cent of the crop. It is known throughout the United 
States, in Europe, Africa, and Asia. 

The grayish-brown leaf -spots ^ which are brittle, irregularly 
circular, and concentrically marked, appear about the time 




Fig. 124. — Little potatoes and aerial pota- 
toes. After Rolfs. 



Vegetable and Field Crops 



227 



the tubers begin to form. The coalescence of the spots 
involves large areas of leaf tissue and results in browned, 
withered leaves, the stems remaining green. The illusion 




— Potato attacked by Corticium. 
After Rolfs. 

is often so complete as to lead the grower to think that the 
vines have died a natural death. The progress of the disease 
is slow, three or four weeks intervening before all the leaves 
are dead. The loss of efficient leaf tissue so diminishes the 
vigor of the plant that the yield is largely reduced. Early- 



228 



Diseases of Economic Plants 



blight is also serious on tomatoes in the South, on leaves and 
on fruits, where it produces a rot. It is found also upon 
eggplants. This is a disease characteristic of dry soils and 
seasons, and is likely to be associated and confounded with 
tip-burn. 

General spraying (p. 236) will hold this blight in check. 
Tip-burn. ^^^' ^-^ — Leaves die at the edges and tips, curl 
somewhat, and eventually the whole top withers. This 

condition occurs when the sun 
is hot and the winds dry, and 
is especially noticeable when 
a cool, wet period is followed 
by hot, dry weather. It has 
been asserted that the primary 
cause is attack by leaf-hop- 
pers. Though not due to a 
parasite, spraying with Bor- 
deaux mixture lessens the loss. 
Wilt -^0' '^'^' ^21 (Fusarium 
oxysporu7n Schl. and Fusarium 
sps.). — This wilt is definitelj^ 
known in many states, and is 
probably identical with a very 
destructive potato disease of 
England, Germany, France, 
and Belgium. 
When the plants are about a foot high, or in mild cases a 
little later, the first trace of the wilt is noticeable. The 
leaves, which are usually light-colored, assume a dull, un- 
healthy appearance, with rolling or curling of the margins. 
Progressive disease gradually causes the top to fall, and 
gives a general effect of premature ripening. When the 
diseased plants are pulled up, the partially dead roots are 
found to be quite brittle, and frequently bear a white or pink 
mold. If the underground portion of the stem is cut across, a 
pronounced brown discoloration is visible. This brown stain 
is also found in the branches leading to the tubers, and a thin 




Fig. 126. — Potato early-blight 
spots enlarged . After Whetzel. 



Vegetable and Field Crops 



229 



slice across the stem end of the tuber will often reveal its 
presence there as well. 




Fig. 127. — Tip-burn. After Wis. Agr. Exp. Sta. 

The loss amounts to millions of dollars annually, due: 
(1) to deficient germination; (2) to early ripening and thus 
to diminished yield; (3) to rot in storage. 



230 Diseases of Economic Plarits 

When the potatoes are dug, there is rarely any external 
evidence of the disease. The major portion of the crop pro- 
duced from wilted plants is nevertheless infected. If these 
potatoes are stored in a cold place, but little change occurs; 
but when infected potatoes are kept in a heated room or 
left out-of-doors in a warm climate, rot soon develops. 

The presence of this disease can be detected, in otherwise 
normal tubers, only by making a thin slice across the stem 
end and searching for the brown discoloration. Such pota- 
toes are not desirable for seed, but are not objectionable for 
food. 

Soils which have once borne a sick crop will infect future 
crops. The general means by which a field may become 
infested are discussed on page 27. In addition to these 
means, the potato wilt is often carried to new fields by seed. 
It is a matter of record that this disease was largely in- 
troduced into California from Oregon by means of infected 
tubers. This could have been prevented by proper quaran- 
tine restrictions. 

If potatoes must be stored for any length of time, all that 
are badly diseased should be rejected, and the remainder 
kept as cool as possible without freezing. It is best to sell or 
consume all affected tubers at once. 

Another very similar wilt is due to Verticillium alhoatrum 
Reink. Several types of tuber rot due to various Fusaria 
are distinguished, e. g., the jelly-end-rot, a soft rot of the 
stem end; dry-rot, also of the stem end. A tuber dry-rot is 
also caused by Phoma. 

Wilt ^^^ (Pseudornonas solanacearum (EFS.)). — This wilt, 
chiefly prevalent from Maryland southward, reported also 
from Indiana, Nebraska, and Iowa, is identical with that of 
eggplant, tobacco, and tomato, and is to a large extent 
transmitted by insects. 

The leaves wilt and dry up; the stems and tubers show 
yellowing and blackening in the veins, and the tubers give 
way to a soft rot. Squeezing the diseased tubers causes ex- 
udation of creamy drops from the diseased veins. 



Vegetable and Field Crops 



231 



Tubers from diseased vines rot rapidly and should not 
be stored. If stored, they should be kept at as low a tempera- 
ture as possible. It is unwise to plant potatoes in land which 
has shown this disease upon any of its hosts, without a long 
intervening rotation. The precautions suggested under soil 

diseases, use of clean 
seed, and special atten- 
tion to insect control, 
are preventive measures. 

Black-leg -^S- ^^l. 284. 285 

(Bacillus phytophthorus 
Appel). — Much confu- 
sion has arisen concerning 
the identity of black-leg, 
since in many instances 
the mere occurrence of 
a black region upon the 
stem near the ground 
line has led to the use of 
the term. It is thus 
probable that in the 
literature of potato mal- 
adies several distinct dis- 
eases have been confused 
with black-leg. 

A distinct, definite, 
and serious disease has, however, been known in Europe 
and England for several years under this name. Jones, 
who studied black-leg in the field in Germany and England 
and what appeared to be the same disease in Vermont, 
described it essentially as follows: The earliest conspicuous 
symptom was that the diseased plants were slightly be- 
low normal size, of a paler or yellowish-green color, the 
lateral branches and petioles becoming more erect and 
the leaf blades curving upward, giving the entire plant a 
narrowed aspect. The lower leaves, in the meantime, have 
possibly shriveled and died. The stem was more or less 




Fig. 128. — Dry-rot caused by Fusa- 
rium. After Coons. 



232 



Diseases of Economic Plants 



browned or blackened from near the surface of the soil down- 
ward. In extreme cases the discoloration was visible 2-3 cm. 
above the soil. The tissues of the discolored part died, and 




Fig. 129. — Potato black-le 



the softer parts decayed. Usually the seed tuber also was 
rotted. Loss as high as 20 per cent is reported in Maine, 
75 per cent in certain fields in Michigan; but such large loss 

is unusual. 

The disease is carried over to succeeding crops in the seed. 



Vegetable and Field Crops 



233 



and is, therefore, of greatest importance to growers of seed 
potatoes. Seed should be carefully selected, and then dis- 
infected. 

Leaf-roll ^^' ^^^ ^^^' ^^^' ^^^ (Phloem-necrosis) and Mosaic 
(Leaf-curl or Curly-dwarf) , two closely related diseases of wide 
distribution, cause serious crop loss. In Bermuda, for exam- 
ple, the loss from leaf-roll is estimated to be well a.bove 50 




Fig. 130. — Potato leaf-roll. After Orton. 

per cent of the crop. The two diseases, formerly regarded as 
three, are difficult to distinguish accurately without the use 
of the microscope, but in general in leaf-roll the segments of 
the lower leaves are pale, permanently rolled upward and 
rigid, the terminal segments becoming spoon-shaped; while in 
mosaic, generally, the leaf segments are distorted, the veins 
unduly prominent, and the blades mottled with light areas, 
and in severe cases the plants dwarfed by shortened inter- 
nodes, giving rise to the designation ''Curly-dwarf." Plants 
affected by either of these diseases show retarded tuber 
development and reduced yield. 



234 Diseases of Economic Plants 

Both diseases are usually of such mild form during the 
first year as to be unnoticed; but appear in much more 
severe form during the second year. Though the causal 
organism is unknown, both are also contagious, and infection 
passes readily from plant to plant in the field. Such infection 
takes place chiefly through the soil and has been observed to 
occur at a distance of 2 meters. The disease is seed-borne and 
probably infestation does not persist in the soil. Therefore 
seed should be taken from a field free of these diseases, or 
seed-plants which grew fully 2 meters distant from diseased 
plants should be selected. 

Minor diseases 

Leaf-blotch ^^^ {Cercospora concors (Casp.) Sacc.) appears 
when the plants begin to blossom. The lower leaves show 
obscurely defined, pale spots, 3-5 mm. in diameter, these 
sometimes blending to form larger areas. The spots some- 
times much resemble the early-blight spot, but more often the 
entire leaf slowly turns yellow and dies. The damage, espe- 
cially to late potatoes, is considerable. 

Leak "^- (Rhizopus nigricans Ehr. and Pythium deharyanum 
Hesse.). — Orton has described a wet, soft rot of potato in the 
peat lands of California. It is characterized by dull brown 
discoloration of the skin and light brown or buff coloring of 
the flesh, accompanied by softening. Upon pressure a clear 
brown liquid without disagreeable odor, exudes. 

The disease spreads rapidly in warm weather, and entire 
shipments may decay en route to market. To prevent infec- 
tion the skin should not be broken in handling, and all refuse 
should be destroyed by fire. Diseased tubers should be scru- 
pulously sorted out of lots intended for storage or shipment. 

Silver-scurf {Spondylocladium atrovirens Harz.). — Dark 
blotches spotted with minute black specks appear on the 
surface of the tubers. Later these assume a silvery-gray tint. 
The disease, recently introduced from Europe, is widely 
distributed, but not of great importance. Infected seed 
should not be used. 



Vegetable and Field Crops 



235 



Black-heart.-^^' -^^ — The centers of the tubers turn black 
or become hollow with a black lining. This is due to ab- 
normal physical conditions, such as high temperature, or 
deficiency of oxygen, and occurs mainly in potatoes stored in 
artificially heated rooms, or piled too deep (over 6 ft.). 
Temperatures above 35° C. (95° F.) should be avoided, and 
ventilation provided. 




Fig. 131. — Black-heart of potato caused by exclusion of air. 

Stewart and Mix. 



After 



Spindling-sprout, the cause of which is unknown, is a 
diseased condition in which the normal stout thick sprouts 
fail to develop and in their stead are slender abnormally long 
sprouts. Seed potatoes affected with this disease result in an 
uneven stand with many missing hills, weak plants, and cor- 
responding decrease in yield. 

Hollow-heart. — In years of abundant rainfall large pota- 



236 Diseases of Economic Plants 

toes frequently show cavities at the centers, lens-shaped 
clefts with browned linings, due apparently to tension result- 
ing from unequal growth. Though this is not a true disease 
such tubers are discriminated against in grading. Varieties 
subject to this trouble should be planted closely since crowd- 
ing helps to overcome the tendency. 

Internal brown-spot, scattered, rusty brown spots, 2-10 
cm. in diameter, occur irregularly throughout the potato. 
No parasite is present and the diseased condition is not trans- 
mitted through the seed. However seed showing this char- 
acter should be avoided. 

Net-necrosis. — Netted, brown or black areas, beginning at 
the stem end, extend through the tuber. The disease is not 
due to parasites and probably affects the yield but little. 
Seed potatoes showing this disease should be avoided. An 
Anthracnose (Colletotrichum) has been described on stems. 

Disease Prevention 

In general to prevent potato diseases: 

1. Plant, if possible, in uninfested soil. 

2. Destroy disease-bearing refuse. 

3. Rotate crops judiciously. 

4. Use only seed free from seed-borne diseases, i. e., scabs, 
black-scurf, wilts. 

5. Disinfect seed in case such diseases as scab and black- 
scurf are present, p. 240. 

6. Spray with 4-4-40 Bordeaux mixture. 

Potato Spraying ^^^' -^^ 

As with other crops, spraying should not be directed or 
planned to meet merely one of the diseases, but rather to 
give the plant the best possible protection against all of its 
enemies. The chief enemies to be met by spraying are 
early-blight, late-blight, and the Colorado beetle or '' potato 
bug." 



Vegetable and Field Crops 



237 



The gains from spraying potatoes with Bordeaux mixture 
as shown in trials at the Vermont Experiment Station, begun 
in 1891 by Jones and extending over twenty years, are shown 
below : 

Gains from the Use of Bordeaux Mixture on Late 

Potatoes 





Sprayed 


Yield per Acre 




Planted 


Sprayed 


Not 
Sprayed 


Gain per Acre 


White Star, 
May — , 1891 
May 20, 1892 
May 20, 1893 
Apr. 26, 1894 

May 20, 1895 
Polaris, 

May 15, 1896 

June 1, 1897 
White Star, 

May 10, 1898 
Average, 
3 varieties. 

May 18, 1899 

Delaware, 

May 23, 1900 
May 25, 1901 
May 15, 1902 

Green Mountain, 
May 1, 1903 

Delaware, 

May 25, 1904 
May 15, 1905 

Green Mountain, 
May 27, 1906 
May 1,1907 
May 15, 1908 

May 28, 1909 

May 9. 1910 


Aug. 26, Sept. 8 
Julv 30, Aug. 13, 25 
Aug. 1, 16, 29 
June 16, July 17, 

Aug. 30 
.July 25, Aug. 13, 31 

Aug. 7, 21 

July 27, Aug. 17, 28 

July 21, Aug. 10 

July 26, Aug. 17, 

Sept. 8 

Aug. 4, 23 
July 20, Aug. 21 
Aug. 1, 20 

Aug. 10 

Aug. 1, .Sept. 1 
Aug. 2, 21 

Aug. 13, 22 

July 16, 25, Aug. 8, 22 

June 26, .Julv 9, 

Aug. 6. 26 
July 12, 23, 
Aug. 6, 27 
July 11, 27, Aug. 15, 

23, 30 


313 bu. 
291 bu. 
338 bu. 

.323 bu. 
389 bu. 

325 bu. 
151 bu. 

238 bu. 

229 bu. 

285 bu. 

170 bu. 
298 bu. 

361 bn. 

.327 bu. 
382 bu. 

133 bu. 

171 bu. 

1.56 bu. 
243 bu. 
240 bu. 


248 bu. 

99 bu. 

114 bu. 

251 bu. 
219 bu. 

2.57 bu. 
80 bu. 

112 bu. 

161 bu. 

225 bu. 

.54 bu. 

164 bu. 

237 bu. 

193 bu. 
221 bu. 

101 bu. 
63 bu. 

65 bu. 

188 bu. 

202 bu. 


65 bu. or 26% 
192 bu. or 194%o 
224 bu. or 196% 

72 bu. or 29% 

170 bu. or 78% 

68 bu. or 26% 
71 bu. or 89% 

126 bu. or 112% 

68 bu. or 42% 

60 bu. or 27% 
116 bu. or 215% 
134 bu. or 82% 

124 bu. or 52% 

134 bu. or 69% 
161 bu. or 73% 

32 bu. or .32% 
108 bu. or 175% 

91 bu. or 140% 

55 bu. or 29% 

38 bu. or 18% 


Average of 20 
years 




268 bu. 


163 bu. 


105 bu. or 64% 



238 



Diseases of Economic Plants 



Extensive experiments were conducted for ten years by the 
New York Experiment Station. The following table taken 
from bulletin 349 summarizes the results: 





At Geneva 


At Riverhead 


Year 


Gain per A. due 


Gain per A. due 


Gain per A. due 


Gain per A. due 




to spraying 


to spraving 


to spraying 


to spraying 




Every Two Weeks 


Three Times 


Every Two Weeks 


Three Times 




Bu 


Bu. 


Bu. 


Bu 


1902 


123.5 


98.5 


45 


27.66 


1903. 


118 
233 


88 
191 


56 
96 


39.5 


1904 


56.5 


1905 


119 


107 


82 


31.5 


1906 


63 


32 


53 


21.5 


1907 


73 . 66 


44 


31 


IS 


1908 


39 


29.5 


15.33 


10.75 


1909 


49.7 


38.7 


52 . 5 


28.7 


1910 


63 


22 


25.5 


14.7 


1911 


93 


40 . 


.5 


1.1 


Average. . . . 


97 . 5 


69 


45.7 


25 



Ten years of business experiments made on farms in order 
to determine the actual profits from spraying under farm 
conditions gave the following results : 











Average 


Average 






Number 


Total 


Average 


Total 


Cost 


Average 


Year 


OF EXPERI 


Area 


Increase 
IN Yield 


Cost of 


PER Acre 


Net Profit 




MENTS 


Sprayed 


Spraying 


FOR Each 


PER Acre 








per Acre 


PER \CRF 


Spraying 








.4. 


Bu. 








1903 


6 


61.2 


57 


$4.98 


$1,07 


$23.47 


1904 


14 


180 


62.2 


4.98 


.93 


24.86 


1905 


13 


160.7 


46.5 


4 . 25 


.98 


20.04 


1906 


15 


225 . 6 


42.6 


5.18 


. 985 


13.89 


1907 


14 


152 . 75 


36.8 


5.90 


1.18 


17.07 


1908 


14 


200 . 25 


18.5 


4.30 


.92 


8.53 


1909 


12 


203.14 


24.4 


4.15 


83.5 


9.55 


1910 


12 


218.5 


19.1 


4.04 


90 


4.39 


1911 


14 


161.6 


18.2 


4.87 


96 


8.09 



In the Geneva and Riverhead experiments, rows sprayed 
three times received Bordeaux mixture with Paris green 
twice and Bordeaux alone once, the dates being July 3, 17, 
and August 3. Other rows were sprayed six times, twice with 
Bordeaux mixture and Paris green and four times with 
Bordeaux alone, the dates being July 3, 17, August 3, 18, 
and September 1, 16. Still other rows were not sprayed at 



Vegetable and Field Crops 239 

all with Bordeaux, but were treated twice, July 3 and 20, 
with Paris green in limewater, to control bugs. The Bor- 
deaux mixture contained 6 pounds of copper sulfate to each 
50 gallons of water, and lime to correspond. Paris green 
was used at the rate of 1 pound to 50 gallons of mixture. 

The recomrhendation of the Geneva Station is: "Com- 
mence spraying when the plants are six to eight inches high 
and repeat the treatment at intervals of 10 to 14 days in 
order to keep the plants well covered with Bordeaux through- 
out the season. During epidemics of blight it may be neces- 
sary to spray as often as once a week. Usually six applica- 
tions will be required. The Bordeaux should contain 4 
pounds of copper sulfate to each 50 gallons in the first two 
sprayings, and 6 pounds to 50 gallons in subsequent spray- 
ings. Whenever bugs or flea l^eetles are plentiful, add one to 
two pounds of Paris green or two quarts of arsenite of soda 
stock solution or three to five pounds of arsenate of lead to 
the quantity of Bordeaux required to spray an acre. 

'^Thoroughness of application is to be desired at all times, 
but is especially important when flea beetles are numerous 
or the weather favorable to blight. Using the same quan- 
tity of Bordeaux, frequent light applications are likely to 
be more effective than heavier applications made at long 
intervals. 

''Those who wish to get along with three sprayings should 
postpone the first one until there is danger of injury from 
bugs or flea beetles, and then spray thoroughly with Bor- 
deaux and poison. The other two sprayings should like- 
wise be thorough and applied at such times as to keep the 
foliage protected as much as possible during the remainder 
of the season. Very satisfactory results may be obtained 
from three thorough sprayings. 

"A single spraying is better than none and will usually 
be profitable, but more are better. 

"Except, perhaps, on small areas, it does not pay to 
apply poison alone for bugs. When it is necessary to fight 
insects, use Bordeaux mixture and poison together." 



240 Diseases of Economic Plants 

Arsenical Injury, due to insecticides, may be avoided by 
applying the arsenicals with lime or with Bordeaux mixture. 

Potato seed disinfection. — The diseases against which 
seed disinfection is effective are only those in which the 
fungus is superficial on the tuber, i. e., primarily against 
common-scab and black-scurf, and against these only under 
certain conditions. Before disinfecting, all tubers obviously 
bearing any other disease should be discarded, as well as 
tubers bearing large black-scurf sclerotia or deep scab pits, 
since the treatments will not kill the fungi on such. Many 
diseases of tubers cannot be detected until the potatoes are 
cut. Before treating, enough of them should be examined 
internally to give satisfaction that the lot is not generally 
infected with any internal disease, as for example, with 
black-leg or wilt. Disinfection should be done before cutting. 
Two chemicals are used according to the following formulae: 

1. Mercuric chlorid (corrosive sublimate). . 4 oz. 
Water 30 gal. 

2. Formalin 1 pt. 

Water 30 gal. 

Mercuric chlorid must not be brought in contact with 
metal; is very poisonous to animals; deteriorates rapidly 
with use, and is more expensive than formalin. The formalin 
solution may be used in any kind of container; grows stronger 
on evaporation, and is generally preferable. 

In either solution the potatoes are soaked for a half hour. 
The solution may be put in a large trough, and the potatoes, 
in crates or bags, set into it, left the requisite time, then sub- 
stituted by another lot of potatoes. Potatoes should be 
dried immediately after treatment. If there is much black- 
scurf present, and no better seed are obtainable, the potatoes, 
if dormant, i. e., not sprouted, may be soaked for two hours 
in mercuric chlorid solution. With sprouted stock the mer- 
curic chlorid is more injurious than the formalin, but the 
formalin is not effective against heavy infection of black-scurf. 



Vegetable and Field Crops 241 

PUMPKIN. See cucumber. 
RADISH. See cabbage. 
RAPE. See cabbage. 

RHUBARB 

Anthracnose -^"^ {C olletotrichum erumpens Sacc.) . — Rotted, 
sunken, soft spots, often several centimeters long, are pro- 
duced on the petioles, and are thickly set in the older portions 
with black acervuli. Though reported as yet only from 
lUinois, the disease is probably widespread, and causes 
considerable loss in the field, and additional loss in shipment. 

Leaf-spot ^^"^ {Phyllosticta straminella Bres.). — Irregular, 
brownish, diseased spots, often several centimeters in diam- 
eter, occur on the leaf blade and bear numerous, minute, 
black pycnidia. Older spots become torn and ragged. 

Crown-rot. — This soft rot of crown and petiole, probably 
due to bacteria, has caused large loss in southern lUinois. 

ROSELLE {Hibiscus sabdariffa) 

Powdery-mildew (Microsphcera euphorbice B. & C, 
Oidiwm).— This mildew of characteristic white, flour-like, 
circular patches has been noted in Florida. 

Flowers of sulfur has proved effective in preventing its 
spread. 

RUTABAGA. See cabbage. 

SALSIFY 

White-rust (Albugo tragopogonis (DC.) Gray). — White, 
rustlike blisters (sori) upon the leaf indicate this disease. 
In late stages of the disease the leaf, near the sori, blackens 
and withers, often tearing lengthwise. 

Soft-rot. — A soft-rot of the roots, resulting in loss of 
green color and prostration of the plants, is attributed to 



242 



Diseases of Economic Plants 



bacteria. The slimy, offensive decay usually begins at the 
lower end of the main root and progresses upward. See 
carrot soft-rot. 

Rust (Puccinia tragopogonis (Pers.) Cda.). — This true 
rust is of somewhat general distribution, but 
is not harmful. 

Powdery-mildew (Erysiphe sps.) is com- 
mon, but not serious. Southern-blight {Scle- 
rotiiim) is injurious in the South. 



SPINACH 



298 



Blight. '-^^ — This is the most destructive 
spinach disease, causing a loss in eastern 
Virginia estimated between $200,000 and 
$400,000 annually. The diseased leaves are 
mottled and deformed, and the plants 
stunted. In general, the symptoms are much 
as in the mosaics with the exception that 
the plants are eventually killed. The disease 
is due to a virus, and can be artificially 
transmitted from plant to plant. In nature, 
infection seems to be carried by plant lice 
(aphids), and not to reside in the soil or to 
be carried by the seed. Spraying to kill the 
plant lice may be the means of conquering 
this trouble. 

Anthracnose {CoUetotrichum spinadoe E. & 
H.). — Blotches appear upon the leaves, first 

Fig. 132.— White- as small, moist, watery areas, associated with 
rust upon sal- slight local wilting, followed soon by the ap- 
pearance upon either side of the leaf of small, 
brown acervuli. The spots then change to 

gray and dry up. The disease spreads rapidly from plant to 

plant and is very destructive both under glass and in the 

open, rendering the plant unfit for use. 

White-smut (Entyloma ellisii Hal.). — The attacked 

plants are unmarketable, due to lack of uniform green color 



sify leaves. 
After Heald. 



Vegetable and Field Crops 



243 



and the presence of pale bleached spots upon the foliage. 
These spots are not definitely limited, nor does the tissue die 
as it does in the case of other spinach leaf spots. 

Black-mold {Cladosporium macrocarpum Preuss) develops 
primarily upon old leaves, and 
renders the plant unsalable. The 
spots are distinguishable from all 
other spinach spot diseases by 
their irregularity, indefiniteness, 
and color. 

To control the three latter 
spinach diseases, it is well to burn 
diseased refuse, practice rotation, 
and employ preventive sprays 
when the plants are young. 
Spraying the edible leaves as the 
plants approach maturity injures 
the sale and is not permissible. 

Leaf- spot (Heterosporium va- 
riabile Cke.). — This disease was 
especially injurious to spinach in 
eastern Virginia during the win- 
ter of 1908-1909, and has also 
been noted in Connecticut. It 
appears early in January and 
continues to increase until the 
spinach season is over. Numer- 
ous leaf spots are produced, at 

first brown, later sooty, as the conidiophores and conidia 
of the fungus develop. The older leaves usually show more 
injury than the younger, but at times all leaves are seriously 
affected. The presence of the fungus renders the leaves 
unsalable, and much additional labor is required at harvest 
time to trim off the injured leaves. 

The disease does not seem capable of attacking healthy, 
vigorous plants, but usually follows injuries produced by 
some other agencies. In Virginia it has been found to follow 




Fig. 133. — Spinach leaf 
spotted by Heterosporium. 
After Reed. 



244 Diseases of Economic Plants 

the injuries produced by Peronospora. Injuries produced by 
cold weather, prolonged rains, insects, etc., undoubtedly 
afford weak points where infection may begin. 

The best preventive measures are to follow general hy- 
gienic precautions, rake up and destroy all dead and diseased 
leaves, keep the injuries from insects and other fungi at a 
minimum, and rotate crops as frequently as possible. 

Minor Diseases 

Downy-mildew (Peronospora effusa (Grev.) Rbh.). — 
Gray to slightly violet, downy spots upon the lower sur- 
faces of leaves, accompanied by pale yellow spots upon the 
corresponding upper surfaces, indicate downy-mildew. The 
disease in its habit and damage resembles that of the grape, 
p. 122. Serious loss is reported from New Mexico and 
Virginia. 

Leaf -blight (Phyllosticta chenopodii Sacc.) affects the 
leaves, especially at their bases, producing spots which bear 
minute pycnidia. Leaf-spot (Cercospora heticola Sacc.) often 
ruins crops by yellowing and dwarfing the plants, thus ren- 
dering them worthless for market. Soft-rot {Bacillus carot- 
ovorus) occurs on spinach in shipment. 

SQUASH. See p. 178. 



SUGAR CANE 



158, 351 



Red-rot (Colletotrichum). — The first external evidences of 
disease are drooping, withering, and yellowing of the upper 
leaves, followed by wilting of the entire crown. Finally, the 
whole stool dies. In less severe cases buds die, and dead, 
black areas extend out from the nodes. The veins running 
lengthwise within the stems are reddened. Uncertainty 
exists as to identity of the causal fungus. The disease is 
one of the most serious affecting sugar-cane. Only healthy 
stock should be used in propagation, and diseased refuse 
should be destroyed. 



Vegetable and Field Crops 245 

Rind-disease (Trichosphrioce sacchari Mass.). — This 
stem disease is first indicated by yellowing and drying of the 
leaves, often followed by death of the plant. The nodes are 
frequently discolored or black. In late stages black pycnidia 
appear on the diseased surface. Diseased refuse should be 
burned and cuttings should be disinfected by dipping in 
Bordeaux mixture. 

Pineapple-disease (Thielaviopsis paradoxa v. Hohn.). — 
This disease originates in cuttings and derives its name from 
the odor of the affected stems. The fungus, which is a 
wound parasite, enters through the ends of cuttings and 
may prevent their germination, or so retard growth that 
worthless plants develop. Dipping the cut ends in Bordeaux 
mixture lessens infection. 

Ring-spot (Lcptosphceria sacchari v. B. d. H.). — Oval, 
gray spots, 3-5 x 5-15 mm., surrounded by narrow brown 
rings, develop in the leaves, and bear minute, black peri- 
thecia. 

Leaf-spot (Cercospora longipes Butler). — Narrow, oval, 
brown spots, about 2 mm. in diameter, surrounded by a 
yellow zone, occur. 

Cacao-disease (Diplodia cacaoicola Hen.). — This is caused 
by a fungus that also grows on cacao. It causes the canes 
to wrinkle. 

Root-rot. This, one of the most troublesome of cane 
diseases, is due to various fungi, one of which is a stink-horn 
(Phallus), another Marasmius sacchari, Wak., both of which 
can be recognized in late stages by the sporophores of the 
fungi. Proper drainage and cultivation, the use of immune 
varieties and healthy stock, the destruction of infected 
refuse, and rotation of crops are helpful. 

SWEET CORN. See p. 283. 

SWEET POTATO -^^ ^^^ 

Soft-rot '■'^^ (Rhizopus nigricans Ehr.). — The most prom- 
inent soft-rot of the sweet potato, the only one that is com- 



246 



Diseases of Economic Plants 



monly met, may be recognized by the soft, wrinkled condi- 
tion of the potato, its sweetisli odor, and usually by the 
presence of a white, later black, growth of mold, appearing 
through the skin of the rotted portion at points of rupture. 
The decay most often begins at one end and passes rapidly 
through the root, but it may start at a wound upon any 




Fig. 134. — Sweet potato soft-rot. 



part of the potato. It progresses with such rapidity that the 
whole potato may give way in a few days after infection. 
Other tubers, if they have broken surfaces or wounds and 
lie in contact with affected ones, will also become infected. 
The rotten roots are therefore often found in groups through- 
out the pile. This rot is sometimes found in the field, but is 
not usually destructive until after digging. The loss in the 
United States in 1917 is estimated at about 5,000,000 bu. 



Vegetable and Field Crops 247 

Normally it cannot enter a sound potato; a wound must 
furnish a passageway. Therefore all wounded roots should 
be laid aside for immediate consumption, and only sound 
roots put in storage. 

Potatoes for storage should be fully matured, carefully 
handled to avoid bruising, thoroughly cured, and kept at 
uniform temperature, 26° to 29° C. (80° to 85° F.), while 
curing, and at 12° C. (55° F.) after curing. Properly ven- 
tilated storage houses should be built when possible. Kiln 
drying at 29° to 35° C. (85° to 95° F.) for 10 to 15 days is a 
good practice. 

It is well to destroy all infective material, rotten roots, 
etc., in or near the storage place, and if the house has been 
infested, to spra^^ its walls and floors thoroughly with a good 
disinfectant, such as Bordeaux mixture or formalin. 

Black-rot (Sphceronema fimhriatum (E. & H.) Sacc). — 
This is among the most destructive of all sweet potato 
decays, causing much loss in storage as well as in the field. 
It is said to equal in damage that of all other sweet potato 
diseases combined. Infected potatoes are bitter and worth- 
less. Black-rot has been reported from nearly all states that 
raise sweet potatoes, also from the West Indies and New 
Zealand. 

The rot may be known by its dark brown to black, irregu- 
lar patches upon the potato surface. These begin as points 
and gradually extend in all directions, involving the whole 
root. Older spots, 2-5 cm. across, often break or crack 
irregularly near the center. This decay differs from the 
soft-rot in that the spots are dry and hard and that it is 
present upon the roots before digging. With a hand lens, 
very small, hairlike, black structures, 1 mm. high, are seen 
studding the centers of the diseased areas. These are the 
beaks of the pycnidia of the causal fungus. 

Upon young sprouts before they are set out the disease 
causes black, dead patches, especially at the base of the 
shoot or even upon the young leaves. The wood of the stem 
may be browned. Such sprouts result in enfeebled plants 



248 



Diseases of Economic Plants 



with diseased roots. The fungus discharges myriads of 
spores into the soil. This disease thus falls under the general 
class of soil diseases. 

In addition to the suggestions given on page 26, especial 

precaution should be exercised to 
avoid sets already infected. Badly 
diseased shoots are easily recognized, 
but the closest scrutiny is needed to 
cull out those only slightly affected. 
Above all, infested seed beds should 
be avoided, and no infected potatoes 
should be used for growing sets. Crop 
rotation should be practiced, and 
every precaution taken to get the 
plants well established in the field. 
A strong, well-started plant will often 
resist the disease where a weak plant 
would succumb. Waite ^^^ says: ''The 
best remedy is to use slip seed. It is 
advisable to grow the crop of vine 
cuttings on new land which is not in- 
fested or on land which has never 
grown sweet potatoes, thus making 
an absolutely clean start even though 
the vine cuttings are taken from an 
infected crop." 

Root-rot ^^'' (Plenodomus destruens 
Hart.). — Small brown or black spots 
appear on the stem near the soil line, 
and eventually girdle the plant, which 
soon wilts. In some regions of Ohio, 
Virginia, and Iowa, losses of 50 per cent 
occur, but the disease is not so widely 
distributed as those mentioned above. 
Texas root-rot (Ozonium). — A firm, brown rot is pro- 
duced on the potatoes. Loss as high as 90 per cent is occa- 
sional. Rotation involving cereals should be adopted. 




Fig. 135. — Black-rot of 
sweet potato. Original. 



Vegetable and Field Crops 



249 



/ 



y/' 



I 



\ 



w 



'i^ 



^i'i-'l 



Soil-rot ^01. 303 .(Cystospora batatce (E. & H.) Ell.). — The 
loss from this rot is sometimes almost total. Due to soil 
infestation the raising of the crop is pro- 
hibited for several years. 

The roots are attacked when quite 
small, sometimes over the whole surface. 
The part infected ceases to grow, while 
adjoining parts enlarge. This results in a 
condition such as that shown in Fig. 136. 
The smallest rootlets are the points of 
attack, thence the disease proceeds to 
the potato and causes the surface spots 
as seen in the illustration. 

The chief loss is in the cessation of 
growth. In badly infested fields no po- 
tatoes of marketable size mature, and 
the crop is not worth harvesting. 

Long rotation to avoid placing sweet 
potatoes upon infested soil is advised. 
Halsted showed that soil-rot, even upon 
land badly infested with the fungus, can 
be controlled by sulfur and kainit; 400 
pounds of each applied to the soil gave 
the best results. Treated plats gave 60 
bushels of clean potatoes as contrasted 
with 5 bushels for the untreated plat. 

Wilt, stem-rot (Fusarium sps.). — In 

this disease, prevalent from the Atlantic 

to Kansas, the leaves turn pale yellow 

and wilt; the stem is blackened within, 

and, later, ruptures. The whole vine 

dies unless supported by roots at some 

other point. Following the death of the 

original stem, the portion of the root still 

alive throws out a fresh growth of short ^^ ...^ o -i 
, , -^ . - Fig. 135. — boil- 

stems and leaves near the center oi the ^.^^ ^f g^eet potato. 
hill. Such efforts at recovery are inef- After Halsted. 



m^j. 



% 



.'J. 



Niv 



i^ 



*i^. 



250 Diseases of Ecoiiomic Plants 

fectual. Losses range anywhere from 10 to 95 per cent of 
the crop, and the total annual loss is at least three-quarters 
of a million dollars. Healthy potatoes must be used for 
seed; the hotbed should occupy uninfested soil, and rotation 
should be practiced. The suggestions given under soil dis- 
eases apply here. 

Minor diseases 

Dry-rot {Diaporthe batatatis H. & F., Phomopsis). — The 
affected part, often the upper end of the potato, becomes 
dry, wrinkled, and covered with numerous pycnidia, the 
flesh within changing to an almost powdery condition. 
Affected potatoes should be destroyed. Java dry-rot ^^"^ 
(Diplodia tubericola (E. & E.) Taub.). — The potatoes show 
dark, shriveled patches with scattered pycnidia. The inner 
tissue is brittle and black. Scurf ^'^•'' (Monilochcetes infiiscans 
E. & H.). — A brown or rusty coat often forms over the 
whole potato. It causes no decay, but does result in shrink- 
ing, loss of volume, and unsightliness, which reduces the 
money value of the crop. Blue-mold rot (PenicilUum expan- 
sum). — The diseased parts, which may involve the whole 
potato, are of almost chalky color and consistency, dry, and 
inoffensive in character. 

White-rust {Albugo ipomoece-pandurance (Schw.) Swingle). 
— White, glistening sori, 1 mm. or so in diameter, appear 
upon the under sides of the leaves and upon the stems. 
These rupture and set loose a mass of powdery, snow-white 
spores. The tissue surrounding the sorus is pale, or yellow, as 
seen from the opposite side of the leaf. Later, brown patches 
result. 

Leaf -blight (Phyllosticta batatas Cke.). — Spots of brown, 
dead tissue from 1-10 mm. in diameter, round or angular, 
are frequent upon the leaf. The}^ are very definitely bordered 
by a dark band, and bear numerous pycnidia, visible to the 
naked eye. In many instances these spots become so nu- 
merous as to cause the whole lea'f to yellow and fall, and thus 
reduce the crop. 



Vegetable and Field Crops 251 

Leaf-spot (Septoria bataticola Taub.) is similar to leaf- 
blight, but with smaller spots. Charcoal-rot (Sclerotium 
bataticola Taub.) is similar in general character to Java dry- 
rot. Rust (Coleosporium ipomoew (Schw.) Burr.). — The 
alternate host is the pine. Rust is injurious in the tropics. 
Trichoderma-'rot {Trichoderma koningi Oud.) and Root-knot 
(nematodes) do some damage. 



TEA 



158 



The diseases of the tea plant are numerous and destructive, 
but since the crop is little grown in the continental United 
States, they ma^- be enumerated, merely, as follows: Gray- 
blight (Pestalozzia) and Brown-blight (Colletotrichiim) spot- 
ting the leaves; Blister-blight (Exobasidium); Thread-blight 
(Stilbum) which kills branches or even the entire plant; 
Copper-blight (Lcestadia) causing copper-colored leaf-spots; 
Red-rust due to the alga, Cephaleurous, Canker due to 
Nectria; Blight due to Marasmius. 

TOBACCO. 

Root-rot ^^' -^^9 (Thielavia basicola (B. & Br.) Zopf.). — 
Known in Europe since 1897, this disease was first reported in 
the United States, in 1904, as occurring upon tobacco, 
though it has probably been long prevalent in tobacco sec- 
tions. It has been noted upon other hosts; namely, violets 
in Connecticut, Maryland, and District of Columbia; 
ginseng in Ohio and New York; also upon begonia, catalpa, 
and clover. Upon tobacco it is now known in Ohio, Con- 
necticut, Kentucky, and North Carolina, and its territory is 
increasing yearly. See also p. 23. 

Root-rot in the seed bed often causes the entire crop of 
seedlings to be discarded, delaying planting or compelling 
a change of crop. In the field the loss sometimes amounts 
to 25 per cent. 

The disease is recognized by the black decay upon the 
roots, sometimes by a cracking and deformation on the stem 



252 



Diseases of Economic Plants 



just above the roots and the failure of the plant to develop 
normally. 

Damping-off due to Thielavia or other fungi may occur in 
seed beds. The plants are attacked when very young, and 




Fig. 137. — Tobacco roots showing effect of root-rot. * 
After Gilbert. 



death may result before they attain a height of more than 
5-10 mm. In other cases of milder attack the roots alone are 
invaded and the plants stunted. The tips of the rootlets 



Vegetable and Field Crops 253 

become brown or black, and the entire root system is in- 
volved later. The decayed roots are brittle and break 
easily. Numerous lateral rootlets are put out to replace 
them, but these also succumb sooner or later. The leaves of 
diseased seedlings on rich soil are usually abnormally dark 
green. They may, however, in poor soil be of a sickly yellow 
color. 

In the field the diseased seedlings may remain without 
growing for weeks; some yellowing, wilting, and dying. 
Others in light soil may survive and yield a fair, but late, 
crop; in heavy soil few survive to be of value. When large 
roots are attacked, the effect is generally limited to the outer 
surface, where a brownish, scurvy appearance is produced. 

Sick plants in uninfested soil or healthy plants set in in- 
fested soil result in' diseased crops, and the development of 
the disease when the causal fungus is present is favored by 
alkaline fertilizers. 

To avoid loss, only uninfected plants from a clean seed 
bed should be used, A seed bed can be rendered safe and 
so maintained by disinfection, by the means suggested 
on page 460, selecting the method best applicable to the 
conditions. Surface firing is the method most widely used in 
connection with the tobacco crop. Formalin and steam have 
also proved efficient in many instances. 

The following measures conduce to reduction, though 
not to complete eradication of the disease: the use of light 
rather than heavy soils for the seed bed ; avoidance of excess 
of water or fertilizer; the use of a new bed each year; avoid- 
ance of too heavy seeding. Infested fields should be given a 
rotation of nonsusceptible crops. A strain of white Burley 
has been developed to a state of high resistance. 

Granville-wilt "^' ^°''' ^^^' ^^^' ^^^ {Pseudomonas solanacearum 
(EFS.) ). — This wilt was first noted in print in 1903 
though known to tobacco growers in Granville County, N. C, 
as early as 1881. It takes possession of the soil, prohibiting 
successful tobacco culture in succeeding years, and in sections 
where tobacco is the chief, possibly the only profitable money 



254 



Diseases of Economic Plants 




73 



n3 



> 

I— t 
O 

IB 
H 

o 

-t-3 

o 



fcC 



o 

o 
o 

O 



00 

CO 



M 



Vegetable and Field Crops 



255 



crop, the advent of this disease has caused great depreciation 
in farm values. 




Fig. 139. — Tobacco plant in early stage of the GranvUle- 
wUt. Original. 

The wilt is now known in North Carolina, Florida, Georgia, 
possibly Connecticut, and what appears to be the same 
disease has been described in Cuba, Porto Rico, France, the 
Dutch East Indies, and Japan. 



256 



Diseases of Economic Plants 



The first indication of the disease is given through the leaves, 
which droop, becoming soft and flabby as though suffering 
from want of water, the leaves remaining green. A typical case 
is shown in Fig. 139. Frequently the leaves on one side of the 

plant succumb earlier 
than those on the 
other side, and even a 
single leaf may show 
one-sided infection. 
The wilted leaves dry 
up, and eventually 
leaves and stalk die, 
though the stalk re- 
mains standing with 
its dead leaves still 
clinging to it. 

At the stage of earl- 
iest wilting a section 
across the stem shows 
a yellowish discolora- 
tion of the woody por- 
tion. In more ad- 
vanced stages, or in 
sections taken lower 
on the stem, the wood 
is found to be pene- 
trated longitudinally 
by black streaks. 
When all the leaves 
are wilted, the wood and bark at the base of the plant are 
blackened and the pith decayed, leaving the stem hollow or 
filled with a soft, rotten residue. If a badly diseased plant 
is cut off near the ground, a dirty, yellowish, viscous exu- 
date issues from the cut wood. 

The root is the seat of the original infection, and any 
plant which shows symptoms in its foliage possesses roots 
already in a pronounced stage of decay. In early stages 




Fig. 



140. — Tobacco plant in late stages of 
the Granville-wilt. Original. 



Vegetable and Field Crops 257 

one root or more may be diseased; in later stages all 
succumb. 

In a series of rotation tests, planned and inaugurated by 
the author,^^^ it was found that growing corn, wheat, cow- 
peas, clover, and mixed grasses, either singly or in rotation for 
a period of five years on badly diseased soil, reduced the loss 
from wilt to an almost negligible quantity. 

The means by which this disease spreads from field to 
field, and methods to prevent such spreading, are adequately 
discussed under soil diseases, p. 26. 

A similar wilt, but due to a Fusarium, has been reported 
from Maryland. 

Wildfire ^^^^ ^'^ (Pseudomonas tabacum (W. & F.)). — 
A bacterial leaf-spot, first noticed in 1917, is widespread 
in North Carolina, Virginia, and occurs also in Wiscon- 
sin. Loss of $100 per acre for entire crops is commonly 
reported. The spot is 2-3 cm. in diameter, often concen- 
trically marked, and has a translucent border surrounded b}^ a 
chlorotic halo. Another bacterial leaf-spot known as An- 
gular leaf-spot (Ps. angulatum (F. & M.)) was also described 
in 1917 as destructive in Virginia. The spots are angular and 
are not surrounded by the halo common in ''wildfire." 

Leaf-spot '^^^ (Cercospora nicotiance E. & E.). — This dis- 
ease, most abundant upon the lower leaves, appears as brown, 
circular spots from the size of a pinhead to a centimeter or 
more in diameter. Older spots bear white centers bordered by 
a darker, raised line, and the centers often fall away, leaving ir- 
regular holes. The whole leaf yellows and ripens prematurely. 

The disease was first described by Sturgis from specimens 
sent from South Carolina, where it was destructive, prac- 
tically ruining the crop. A damage of $1000 to one crop 
alone was noted. The use of Bordeaux mixture early in the 
season is permissible and advantageous. 

Bed-rot {Corticium vagum) . — Damping-off and rot of 
seedlings occur in the seed bed. The causal fungus may often 
be seen as spots of web-like white mold upon the ground 
around the affected plants. The general characters and 



258 



Diseases of Economic Plants 



prophylaxis are discussed under damping-off, p. 19. Seed 

beds known to be diseased 
should be avoided unless 
previously disinfected. 

Drop ^^^ (Sclerotinia liber- 
tiana) . — Damping-off due 
to Sclerotinia is reported as 
a common trouble in seed 
beds. The injury to the 
plant is similar to that of the 
usual damping-off while the 
fungus presents the charac- 
ters described under lettuce- 
drop. Young plants are 
killed ; older plants may sur- 
vive, and if set in the field, 
develop poorly. 

Mosaic. ^^^' ^^^ — Wher- 
ever tobacco is grown the 
mosaic is very widely dis- 
tributed and destructive. 
Depreciation of $50,000 in 
quality was attributed to it 
in Ohio in 1905. It pro- 
duces a mottled appearance 
of the leaves due to varia- 
tion in texture and green- 
ness ; parts of the leaf show- 
ing full green and normal 
thickness, other spots pale 
or yellowish green, and thin. 
Accompanying these signs 
are distortions due to un- 
equal growth, wrinkled or 
curled leaves, and leaves of 

one-sided growth. Slightly affected leaves are depreciated in 

value; badly diseased leaves are worthless. 




Fig. 141. — Tobacco leaf showing 
leaf-spot. After Conn. Agr. 
Exp. Sta. 



Vegetable and Field Crops 259 

The cause of mosaic is unknowr), but it has been repeatedly 
shown experimentally that it can be communicated from 
plant to plant by first touching a diseased plant and later 
touching a healthy^ one. The disease then appears within 
six to fourteen days. Thus the disease is spread largely by 
topping. In nature it is probably spread by insects. The 
virus appears to be present in all parts of an affected plant, 
even in the trichomes, and, when inoculated locally, spreads 
rapidly throughout the plant, though the disease is not 
transmitted to the offspring through seed from diseased 
capsules. Tomatoes, petunia, physalis, datura, solanum 
(but not the potato), and pepper are susceptible to inocula- 
tion from tobacco plants. 

The seed bed should be either new or thoroughly disin- 
fected by steam or firing, and no tobacco refuse or tobacco 
water used on it. Diseased seedlings in the bed, if any ap- 
pear, should be destroyed. It is well to top, worm, and 
sucker the healthy and sick plants separately, on different 
days, thoroughly washing the hands with soap and water 
before passing from the diseased to healthy plants. 

Orobanche. — This is a true flowering plant, which draws 
its nourishment from the roots of the tobacco plant to which 
it is attached. The orobanche occurs in small clusters, its 
stalks are from 1-4 dm. tall, and entirely devoid of green 
color. 

They should be pulled and burned before they produce 
seed. Root-knot (nematodes), see p. 24. 

Curing-house '* diseases." — When tobacco is cured by 
natural heat, various rots may occur. Among these are: 
Stem-rot, due to various fungi; Pole-rot, consisting of small, 
blackened areas upon the leaf, limited at first to the regions 
near the veins. These spots may enlarge within two days to 
cover whole leaves, and the contents of the entire barn may 
become worthless, the leaf having become so wet and soft 
as to readily fall apart. The cause of these rots is not cer- 
tainly known; indeed there may be several separate or- 
ganisms, each capable of inducing such rot. 



260 Diseases of Economic Plants 

These troubles can largely be controlled by proper regula- 
tion of the moisture and temperature conditions, i. e., by 
building such barns that outside air, when too damp, can be 
excluded, and yet with proper provision for ventilation to 
carry off the moisture from the drying tobacco. 

Wet-butts is due to freezing before curing is complete; 
White-vein to rapid drying; Black-rot (Sterigmatocystis 
nigra v. Tieg.) occurs during the sweating, the tobacco turn- 
ing black and losing its proper texture. It is brought about 
by too high moisture content. 



TOMATO. 



314, 341 



Bacterial Wilt, blight (Pseudomonas solanacearum (EFS.) ). 
— This disease of the tomato is widespread, especially in the 
South, and prohibits tomato culture upon many thousands of 
acres of land. It occurs especially in the states south of 
Maryland, and has also been noted in New Jersey, Delaware, 
Ohio, and Colorado. 

The leaves wilt, either singly or throughout the entire 
plant at once; growth stops and the plant dies. The stem 
appears at first dirty green, then brown, then black. It soon 
shrivels, and the veins become brown and show as narrow 
black lines, or in section as black dots. The wilting of the 
foliage and the blackening of the vascular bundles are dis- 
tinctively characteristic. 

Soil bearing diseased plants one season remains infested 
during succeeding years and must be abandoned for tomato 
culture. The disease is spread from plant to plant largely 
by the potato bug (Colorado beetle) and other insects. 
For this reason all leaf-infecting insects should be given 
special attention. In other respects this disease in symp- 
toms, cause, dissemination, and treatment is similar to 
the usual soil diseases. 

Another wilt, similar but of slower development, is de- 
scribed as caused by Bacterium michiganense EFS.^.^^ 

Wilt ^^^ (Fusarium lycopersici Sacc. and Fusarium sps). — 
This wilt is also widespread. It occurs not infrequently 



Vegetable and Field Crops 



261 



as the cause of partial or even total losses of the crop. 
The plants usually reach considerable size, blossom, and 
set fruit before showing the disease, which first appears 
in the field on single plants, generally sickly looking, and of 
unhealthy color, followed by symptoms of wilt. In the 
worst cases all of the plants die before the end of the growing 
season, sometimes quite suddenly at the last; or the crop 
may mature with plants missing more or less extensively. If 
a badly affected or dead plant be pulled up, the roots are 




Fig. 1 i2. — Tomato iiekl sliowiag effect of wilt. 

found to be decayed. If a plant is pulled up as soon as it 
begins to show wilting, the roots look healthy and sound, 
but close inspection shows that many of the larger laterals are 
decayed at the ends. The disease consists of a dry rot of the 
roots, commencing at the ends and working upward. 

The first symptom is a pale yellowish color of the lower 
leaves, which soon dry from the tip toward the base without 
spotting. The veins and woody portion of the stem are 
darkened, especially upon the side bearing the diseased 
leaves. 

As to means of dissemination and control, what is said 
under soil diseases will applj^ 



262 



Diseases of Economic Plants 



Leaf -mold {Cladosporium fulvum Cke.). — Under glass 
in the North and occasionally in the open, especially in the 
South, this disease is destructive. It occurs as rusty or 
cinnamon brown blotches on the lower side of the leaf, which 

turns yellow above, then 
brown or black, curls, and 
dies. The loss of food 
supply consumed by the 
parasite, together with the 
loss through destruction 
of the leaf green, injures 
the yield seriously. 

Indoors ventilation is 
the best remedy, coupled 
with clean culture to avoid 
carrying the pest over to 
another year. On fields 
Bordeaux mixture would 
doubtless serve well. 

The causal fungus of 
this disease was first de- 
scribed in 1883 by Cooke 
from specimens collected 
in North Carolina. 

Leaf-spot ^^^ (Septoria 
ly coper sici Speg.). — A 
very common leaf-spot 
has almost precisely the 
general appearance illus- 
trated in Fig. 143, except 
that small pycnidia occupy the spots. It is known through- 
out the United States, South America, Europe, and Australia, 
and often causes large loss. In some states it is the most 
important tomato disease. The total loss in the United 
States is estimated as $5,000,000 annually. 

The disease attacks the older leaves first and proceeds 
toward the top of the plant, often causing the loss of so 




Fig. 143. — Tomato leaf showing 
spots of mold. 



Vegetable and Field Crops 263 

many leaves as to give the plant the appearance of blight, 
and resulting in complete ruin of the crop. The presence 
of the leaf-spot distinguishes this from any of the blights. 
Spraying with Bordeaux mixture is effective against this 
disease though valueless against the various wilts. Especial 
attention should be given to guard, by spraying, the seedlings 
in the seed bed, using a wea^k Bordeaux mixture. Moving 
among the plants when they are wet spreads infection. All 
refuse should be burned or plowed under. 

Downy-mildew, late-blight ^^^ (Phytophthora infestans 
(Mont.) De Bary). — Arising from the same cause as the 
dreaded potato blight, of which host the tomato is close kin, 
is the tomato blight which causes large loss of the crop in 
some sections of California. It has been reported also in 
Massachusetts and Colorado. 

As with the potato, the amount of damage is closely 
dependent upon weather conditions, the disease being greatly 
favored by a warm, humid atmosphere. It appears suddenly 
as dark, discolored spots on the fruit and other green parts. 
On the fruit the spot, usually upon the upper side, is watery 
and large. Many tomatoes, apparently healthy when 
picked, rot in shipment, the rot being accompanied, under 
humid conditions, by a fine, white surface mold. Dark spots 
upon stems and branches soon extend throughout the whole 
plant, giving it the appearance of one stricken by frost. 

Protective spraying with 5-5-50 Bordeaux mixture, as 
recommended for the potato, will probably serve in case of 
this disease. In regions of infrequent rainfall it is neces- 
sary to spray only after each rain. 

Fruit-rot ^^^ {Phoma destructiva Plow.). — Leaf-spots are 
present, but it is as a spot upon either green or ripe fruit that 
greatest injury is incurred. The spots are 1-3 cm. in diam- 
eter, brownish-black, and depressed. This trouble is most 
prevalent on tomatoes, originating in the South, and shipped 
to northern markets, and on such fruits causes heavy losses. 

Blossom-end rot. — Readily recognized from its name, 
this troublesome disease is essentially a dry, black rot ap- 



264 Diseases of Economic Plants 

pearing on the blossom end and injurious chiefly to early 
tomatoes. It is especially harmful, owing to the high value 
of the early fruit that it destroys. Various factors have been 
named as the cause, and it cannot yet be said with certainty 
which is responsible. 

The trouble is more serious upon droughty soils and can 
to some extent be controlled by irrigation or moisture con- 
servation, i. e., increasing the water-holding power of the 
soils by the addition of organic matter and surface tillage. 

Early-blight (Alternaria solani (E. & M.) J. & G.). — 
Ruin is brought to the crop in many seasons, particularly 
in the southernmost states, by this blight, which is identical 
with the potato early-blight. The leaves bear numerous, 
small, usually angular spots, often concentrically marked, 
which appear first as minute brown specks, later showing a 
pale center with a darker border. In badly affected leaves the 
tips dry and curl up. Petioles and stems are also attacked. 

Thorough spraying with the usual Bordeaux mixture should 
be begun at the first indication of the disease and continued 
weekly, or semiweekly if growth is rapid and the weather 
damp. Often it is still better to begin spraying in the seed bed. 

Southern-blight (Sclerotium rolfsii Sacc). — This blight 
IS often completely destructive to the tomato in the south- 
ernmost states. The first sign is wilting of the terminal por- 
tion of the plant, distinguishing Southern-blight from other 
wilts, which commence with the lower leaves. 

For discussion and treatment, see pepper. 

Leak {Rhizopus nigricans) . — The effect is much as on 
strawberries and the loss during shipment is large. 

Minor diseases 

Anthracnose (Colletotrichum phomoides (Sacc.) Chest.). — 
This is chiefly a disease of the ripe fruit, either upon the vines 
or after harvest. It appears as sunken, discolored spots with 
wrinkled surfaces and black specks, the acervuli. The disease 
does much damage to fruit before it is picked, and also in- 
jures the keeping quality. 



Vegetable and Field Crops 



265 



Sooty-mold {Fumago vagans Pers.). — Dense, olive-black 
growths of mold form upon the leaves. Damping-off occurs 
in the seed bed. Timber-rot (Sclerotinia), see lettuce. 
Buckeye-rot (Phytophthora terrestria) is a zonate, hard rot of 
fruit. Winter-blight. — Loss of S2,500 in one house is re- 
ported, but the disease is not generally distributed. Develop- 
ment is dwarfed, and the stems show brown lesions in cortex 
and bundles, but no parasite has been demonstrated, Ro- 
"sette ^^^ {Corticium vagum). — This is identical with the 
potato black-scurf, showing 
similar lesions upon the root 
and stem near the ground. 
The tops have long inter- 
nodes and dwarfed leaves 
which are somewhat curled. 

Upon the ripe fruits, espe- 
cially those touching the 
ground, this disease occurs 
as a brown rot upon a 
slightly wrinkled epidermis. 
Hollow-stem appears to be 
due to improper growth con- 
ditions. Blossom-drop is due to unknown cause. Leaf-roll is 
similar to that of potato. Root-knot (nematodes) is common. 

(Edema.^^^ — This is a condition of overgrowth of certain 
cells of the plant, causing swelling of veins and leaf tissues, 
and curling of the leaves in irregular growth. Usually 
confined to the greenhouse, it is caused by excess of water, 
lack of light, improper temperature, and especially by over- 
heated soil, and is readily controlled by careful management. 

Chlorosis. — The leaves show completely whitened areas. 
The cause is unknown. Mosaic. — Upon the tomato appears 
a mosaic, similar to that of tobacco. Aside from this ap- 
parent kinship little is known about it. 

TURNIP. See p. 165. 




Fig. 144. 



— Tomato anthracnose. 
After Heald. 



WATERMELON. See p. 178. 



CEREALS 

Cereal Smuts in General ^^^ 

Dark or black masses usually dusty, though sometimes 
compact, replace floral parts, grain, glumes (chaff), or in 
some cases involve the leaves and stem. The smut mass con- 
sists almost wholly of the spores of the causal fungus which 
gains entrance to the plants when they are in a susceptible 
condition of development, the time varying with different 
kinds of plants, and grows within the plant as an active 
parasite, drawing its nourishment from its involuntary host. 
When the host plant has attained the right age, and corre- 
spondingly, too, the fungus has reached its proper stage of 
maturity, the disease becomes apparent to the eye as the 
familiar smut. 

Smut spores under suitable conditions of moisture, food, 
and heat sprout, and produce smaller spores, sporidia, 
which, if they fall upon the right host plant in the proper 
period of its development, penetrate into it and grow. 
The host plant may or may not outgrow its enemy. In 
any event, its presence is not apparent to the naked eye 
until the period of maturity arrives again, and another crop 
of dark-colored spores is produced. 

Kinds of smut.^-^ — In all, something more than 600 
species are now recorded. Over 205 of these are found in the 
United States, growing upon some 442 different kinds of 
plants, most of which are unimportant and wild; although 
some of them, such as the corn smut, onion smut, and the 
smuts of wheat, oats, rye, barley attack plants of high eco- 
nomic value and cause great damage. The yearly toll 
from three of these that are easily preventable has been 
estimated to be as high as 25,500,000 bushels of wheat, 
110,000,000 bushels of oats, 6,000,000 bushels of barley. 

266 



Cereals 267 

Negligence thus involves a total of more than 100,000,000 
bushels of grain annually. 

The common corn smut develops upon any part of the 
corn plant, but is usually most conspicuous upon the ear and 
tassel. Another smut of corn growing only upon the tassel 
is less widely known. Rye smut develops mainly in the 
stem; the smut of oats, wheat, and barley in the ovary, 
the grain; onion smut grows upon the leaves, often in 
the bulb. 

It is evident that to know precisely what parts and at 
what periods the various crop plants are open to infection 
is of utmost importance in looking to the prevention of the 
smuts. It was earl}^ proved that oats are susceptible to 
infection only in the early stages of their development. 
The exact work of Brefeld proved that corn is susceptible to 
infection on all young, tender, growing parts, and in 1896 
Maddox, Brefeld, and others showed that in the case of the 
loose smut of wheat and the barley smut infection occurs 
while the plant is in bloom, this infection affecting the seeds 
and resulting in smutted plants in the crop raised from such 
infected seeds. 

It is upon these facts that our present modes of preven- 
tion are based. The treatment for oat smut is such as to 
kill the spores adhering to the grain and thus prevent in- 
fection during the period of susceptibility, i. e., the very 
young seedling condition. The same treatment is effec- 
tive for the stinking smut of wheat. The loose smut of 
wheat gaining entrance to the plant before the grain is 
harvested cannot be prevented by such means without 
danger to the seed, but can be prevented by the use of clean, 
uninfected seed. Corn, being susceptible at all ages of its 
growth, cannot be protected by seed treatment. 

Owing to their great damage and conspicuousness, smuts 
have attracted attention from very early times, and many 
references to them are found in ancient writings. Probably 
not until 1791, however, was their true nature as vegetable 
parasites recognized. Many were the means that were 



268 



Diseases of Economic Plants 



suggested for the prevention of these pests: placing laurel 
branches in the field, change of seed, avoidance of manures, 
thorough screening, soaking in brine, etc. 



V}\ 



"/'V 



'■'')' ' /i 



* I! 







Fig. 145. — Oat plants, smutted and healthy; note 
difference in height. 

Preventive treatments. — One early remedy that has 
proved its value and remained in common use, soaking the 
seed in copper sulfate, was first tried by Tessier in 1789, after 
he, in 1786, and Young, in 1787, had tested numerous chem- 



Cereals 269 

icals. His test was without results, since, during the season 
of his experiment, neither treated nor untreated wheat was 
smutted. Prevost of France in 1807 was the first to publish 
an account of the successful use of copper sulfate for wheat 
smut. He recommended a solution of about 6 per cent 
strength, and the remedy was, and is, still widely used. Solu- 
tions varying in strength have been employed, one-half per 
cent being most highly recommended. In 1873 Dreisch 
improved the copper-sulfate treatment by using limewater 
following the copper sulfate; thus, to a large extent, diminish- 
ing the amount of seed killed by the treatment. 

Jensen, a Dane, in 1887 and 1888 reported excellent 
results with oat, barley, and wheat smuts from dipping 
the seed in hot water. Untreated seed gave 36 per cent of 
smut. One-fourth per cent of copper sulfate gave one-half 
per cent smut. Warm water, 56° C. (133° F.) for five minutes, 
gave no smut. Kellerman and Swingle soon afterward in- 
troduced this last treatment into this country. 

In 1888 the germicidal action of formalin was discovered 
and this substance was used as a preventive for oat 
smut by Bolley of North Dakota during the years 1894 
to 1897.3-1 

The use of the various smut remedies is usually attended 
by an increase in vigor of the plants, and by an increase 
in jdeld in excess of that due simply to the elimination of 
the smutted grains. Thus increases of over 4 bushels per 
acre have been found in wheat fields in which only about 
\]/2 bushels were destroyed by smut. Similarly, with oats, 
the increase in yield is often five times as great as the quan- 
tity of grain lost by smut in fields not treated. This may 
be due to elimination of the fungus from plants which other- 
wise would have to resist it throughout a portion of their 
growth period or it may be due to the killing of spores of 
numerous fungi other than those of smut on the seed which 
exert an adverse influence during and following germination. 
An excellent account of the early history of smuts in general 
may be found in the Report of the Kansas Agricultural 



270 Diseases of Economic Plants 

Experiment Station for 1889, and a comprehensive article 
upon corn smut in the Twelfth Report of the Indiana Agricul- 
tural Experiment Station. 

Present methods of seed treatment.^^^- ^^^ — Preliminary 
to any form of seed treatment, the seed should be thoroughly 
cleaned, in some cases floating-out of the spore-filled grains is 
necessary, and after treatment it should be protected from 
contamination. Sacks, bins, drills, etc., with which seed will 
come in contact, should be disinfected with formalin. 

The common methods of cereal seed treatment now are by 
formalin, hot water, or copper sulfate. The first is simpler and 
easier and is preferable whenever it is effective. In treating 
for certain kinds of smut, however, the formalin treatment is 
not so effective as is the hot-water method. These three 
methods with their limitations are as follows: 

The formalin wet method. — The seed to be treated is 
either dipped in the solution of formalin, 1 pint to 30 or 
40 gallons of water, or this solution is sprinkled on the seed, 
with thorough mixing, at the rate of one gallon to each 
bushel of seed. The pile is then blanketed and later spread 
out to dry. 

In a modification known as the formalin dry method ^'-^ the 
seed is shoveled from one pile to another and each shovelful is 
sprayed or sprinkled with a solution consisting of, formalin 
(37 per cent formaldehyde) diluted with an equal amount 
of water, and applied at the rate of one quart (1 pint of 
formalin) to 50 bushels of seed. A quart sprayer is conven- 
ient for use. After treating, the seed should be blanketed 
for five hours, when it is ready for planting. Workmen 
will find the formalin irritating to the mucous membrane, 
and therefore should apply the solution as directly as possi- 
ble to the seed. A variation from this method is to mix 1 
pint of formalin with 10 or 12 gallons of water and sprinkle 
on the seeds as they are shoveled over. They may then be 
sacked immediately and sowed next day. This method, 
employing a strong solution, seems to be both safe and 
efficient with oats, but its use with wheat and other grains is 



Cereals 271 

still in the experimental stage and is apparently attended with 
danger to the seed. 

On a large scale, oats may be treated by the formalin 
method at the rate of 500 bushels an hour, by throwing the 
formalin solution, by means of a steam pump, against the 
grain as it falls through elevators arranged with deflectors so 
as to give proper con t act. ^"^ 

The formalin treatments as above given are effective 
against those smuts in which the spores lie upon the surface 
of the seeds and in which the smut fungus is not within the 
seed itself, e. g., oat smuts, wheat bunt, covered smut of 
barley and rye, rice smut, sorghum, and millet kernel-smut. 

Long time formalin treatment. — Seeds are immersed for 
two hours in the formalin solution, 1 pint to 40 gallons of 
water. Favorable results are reported even in those cases of 
floral infection where the hot-water treatment was formerly 
thought necessary, e. g., in the cases of wheat loose smut and 
the covered smut of barley, but complete reliability of this 
treatment for these diseases is not yet demonstrated. 

Copper-suifate treatment. — This is the oldest effective 
treatment of cereal seeds. It has, however, on account of its 
greater cost and the larger injury done to the seed, in the 
main been superseded by formalin methods. It is effective 
against the same smuts for which formalin is used, but is 
recommended only where there is heavy soil infestation. A 
solution of 1 pound of copper sulfate and 1 pound of common 
salt to 5 or 10 gallons of water is used, and the seed either 
soaked, sprinkled, or dipped. Treatment should be com- 
pleted by dipping or sprinkling with milk of lime (1 pound of 
quicklime to 10 gallons of water). 

The hot-water treatment ^^^ is employed for those smuts in 
which the fungus is within the seed, not superficial. There 
are three forms: 1, the short treatment; 2, the modified hot- 
water treatment; 3, the long treatment or pasteurization. 
The first consists, in general, in subjecting the seed to water 
at a temperature ranging from 52° C. (120° F.) to 61° C. 
(142° F.) for 10 to 15 minutes. It is of use in only those 



272 Diseases of Economic Plants 

cases where formalin can be used, and will therefore not be 
described further. The directions for the modified hot-water 
treatment, drawn from Freeman and Johnson, ^'-^ with slight 
changes, are as follows: 

After the seed has been cleaned by thorough fanning and 
sifting, it should be soaked for from five to seven hours 
in water at ordinary room temperature, 17° to 22° C. (63° 
to 72° F.), then placed in small, loose sacks or wire baskets, 
containing not more than one-half peck each, and drained 
for a short time. The seed must be treated in small lots 
in order that all of the grain may quickly and uniformly 
reach the desired temperature. Two tubs or vats of water 
should be provided. In one tub (No. 2) the exact tempera- 
ture required should be maintained. The other tub (No. 1) 
is used for bringing the grain to the temperature of the 
treatment, so as not to lower the temperature in tub No. 2. 
Galvanized iron tubs of 20 to 40 gallons capacity, and 
kerosene or gasoline double-burner stoves, are convenient. 
The drained sacks or baskets of seed should be plunged into 
tub No. 1 for a minute, then transferred to tub No. 2, and 
kept agitated while immersed at temperatures and for the 
periods specified below, the temperatures mentioned being 
maintained as nearly as possible: For barley, 13 minutes 
at 52° C. (125.6° F.); for wheat, 10 minutes at 54° C. 
(129.2° F.). In treating barley, if the temperature should 
rise above 52° C. (125.6° F.), the time of immersion must 
be reduced to ten minutes at 53° C. (127.4° F.), or five min- 
utes at 54° C. (129.2° F.). Above 54° C. (129.2° F.) there 
is no safe margin. If the temperature falls slightly below 
52° C. (125.6° F.), the time of treatment should be increased 
in proportion. A temperature lower than 51° C (123.8° F.) 
is not effective. In treating wheat, if the temperature should 
rise above 54° C. (129.2° F.) or fall below 52° C. (125.6° F.), 
the time for immersion must be diminished or increased ac- 
cordingly. Under no circumstances should a temperature of 
more than 55° C. (131° F.) be allowed. Temperatures be- 
low 51° C. (123.8° F.) are ineffective. A reliable thermometer 



Cereals 



273 



is necessary, since the use of an inaccurate instrument may 
result in injury to the germinating power of the grain or in 
failure to prevent the smut. At the end of the period of 
treatment, the grain should be transferred to a cold bath to 
terminate the action of the heat. 

Two men working together can easily treat one bushel 
of grain an hour, or enough seed in one day to sow a seed 



waterS-r 





( jBoiling water. 
Post. 




Fig. 146. — Diagram showing a convenient arrangement of utensils for 
the Jensen hot- water treatment. After Swingle. 



plat of from 6 to 10 acres. The seed may be dried by spread- 
ing it out in thin layers, not over 5 cm. in depth, on a clean 
granary floor or on canvas, and shoveling or raking it from 
time to time. It should not be allowed to sprout. Care must 
be taken to prevent freezing of the grain when it is moist, 
as this will impair germination. 



274 Diseases of Economic Plants 

Seed treated as indicated may be planted as soon as it is 
sufficiently dry to run freely through the drills, making al- 
lowance for the swollen seed. 

The long hot-water treatment or pasteurization consists in 
subjecting the seed to a temperature of 45° C. (113° F.) for 
three hours, the permissible range being 44° to 46° C. (111° to 
115° F.). The advantages of this method are greater effi- 
ciency, less danger of killing the seed, and the need of but a 
single bath. It is difficult, however, to maintain the proper 
temperature for so long a time. 

These hot-water treatments, though effective against both 
smuts of wheat and of barley, are used primarily for the loose 
smuts of barley and wheat, and are generally combined with 
the seed-plat, see p. 275, and rogueing. Hot-water treat- 
ments are much simpler and more accurate of application 
if steam is available for heating purposes. 

Injury to seed by treatment. — The germinating power of 
treated seed should be tested, and if low, the rate of planting 
should be correspondingly increased. The formalin treat- 
ment does but inappreciable injury to sound seed, though 
cracked seed are injured by chemicals. The softer wheats are 
more often cracked than the harder varieties, therefore are 
more liable to injury by chemical treatments. Seed sub- 
jected to wetting may be injured in germination power if 
dried too slowly. However, poor stands attributed to seed 
injury often are really due to the use of too little seed, since 
the treated, swollen grain feeds more slowly through the drill. 
The sensitiveness of various seeds ^^^ to treatments is 
indicated in the following table. shows no injury, tr a trace 
only, H — I — h very serious, -\ — f- less serious. It is to be added, 
however, that some experimenters report injury to wheat from 
the dry treatment. 

Wheat Rye Oats Barley 

Formalin 

Dip 

Sprinkle 

Dry 

Soaking 1 hour 



Cereals 275 

Wheat Rye Oats Barley 

Copper sulfate 

10 minutes • + + + tr 

Long time + + + + + + 

Hot water 

133° 12 minutes + + + + + + tr 

101-115° 3 hours tr tr 

Modified 

129° 10 minutes + + tr 

The Seed Plat. — A good, clean, well-cultivated piece of 
land should be selected for raising seed. The plat should be 
large enough to provide at least twice as much grain as will be 
necessary for farm seed the following year in order to allow 
for loss in cleaning and selecting. This seed plat should not lie 
near fields of smutted crops of the same cereals, nor should 
it be so located that the prevailing winds at flowering time 
can carrj^ spores to the seed plat from a neighboring field 
of the same grain. This isolation is absolutely necessary. 
A strip of wood, a cornfield, or a large meadow is a valuable 
protection. In this plat should be planted seed treated by 
the hot-water methods. The seed plat may be maintained 
from year to year, as long as any smut is present in the grain 
fields. 

Cereal Rusts in General ^-^ 

The rusts constitute a complex, intricate, difficult, but 
interesting group of diseases. It is said that the ''average 
annual loss from rust throughout the United States far 
exceeds that due to any other enemy, insect or fungous, 
and often equals those from all others combined." 

The black-stem-rust alone in the United States and 
Canada in 1916 was estimated to have caused a loss of about 
280,000,000 bushels of wheat and additional loss on oats, 
barley, and rye. 

The rusts in their most complete form exhibit three dis- 
tinct stages (cf. p. 150). The spring stage, or cluster-cup, 
consists of a group or cluster of very minute, cup-like, spore- 



276 Diseases of Economic Plants 

bearing regions. These cups are sunken in the tissue of the 
host, often with their rims only protruding. The second, or 
summer, stage, also called the uredinial stage, is of entirely 
different appearance, consisting usually of elongated sori, 
bearing a mass of spores the color of iron rust or verging 
toward orange or yellow. These spore masses are at first 
covered by the epidermis of the host, but this covering 
eventually ruptures, disclosing the usually dusty or pul- 
verulent mass of spores, surrounded by a fringe of the re- 
maining epidermis. The third, winter or telial, stage consists 
of sori almost exactly like those of the uredinial stage except 
that the spores within are usually darker in color and in 
a compact, cushion-like mass. The sorus is often identical 
in the two latter stages, a uredinium gradually changing as 
the season advances into a telium. 

These three stages have, in general, three separate func- 
tions. The function of the teliospores is to live over winter 
or over the long resting period of the fungus. They are 
essentially long-lived and hardy. The cluster-cup spores 
multiply and spread infection, especially in the earliest part 
of the season. The urediniospores continue the multiplica- 
tion and infection throughout the growing season of the host. 
The last two forms of spores are in general comparatively 
short-lived. If the host plant remains alive over winter, as is 
the case with winter wheat, the fungus, in the South, may 
continue to grow and produce summer spores throughout 
the winter. Even in colder climates the urediniospores 
of some rusts live over winter and start infection in the 
spring. 

In the case of some rusts these three forms are all known 
to be present. In the case of other rusts one stage or even 
two stages may either be unknown or may not exist at all. 
When all three stages do exist, the spring stage often develops 
upon some host other than that bearing the uredinial and 
telial stages. Thus the spring stage of the wheat rust is 
found upon the barberry; of corn upon oxalis; of oats upon 
buckthorn. 



Cereals 



277 



That some intimate relation existed between the bar- 
berry bush and the black-stem-rust of wheat was suspected 
very early in the seventeenth century, and in 1660 a barberry 
eradication law was passed in France, while between 1726 and 
1779, Connecticut, Rhode Island, and Massachusetts did like- 
wise. In 1818 Schroeter, a Danish school-teacher, published 
man,y observations concernin^e; the relation of the cluster-cup 
upon the barberry and the rust of grains. This relation was 
finall}' definitely proved b}^ De Bary in 1865, who, by sowing 
the teliospores from the wheat upon the barberry, produced 
the cluster-cups. 

Some rusts are closely limited in host range and can grow 
on very few, perhaps on only one host ; others are able to grow 
on various hosts. The host relation of several important 
cereal rusts is shown in the following table : ^^^ 













33 


53 






■*o 






55 






Also on other genera of grasses 






CO 

O 
tr 


1. 






+ 


as below 


Puccinia 





+ 


+ 





Agropyron sps., Elymus 3 sps., 


graminis 














Hordeum 4 sps., Hystrix 1 sp., 


secalis 














Secale 1 sp., Sporobolus 1 sp., 
Bromus 2 sps., Avena saliva and 
Triticum, vulgar e. 


Puccinia 


+ 





tr 


+ 





+ 


Agropyron 7 sps., Elymus 5 sps.. 


graminis 














Hordeum 5 sps., Hystrix 1 sp., 


tritici 














Siecale 1 sp., Triticum 8 sps., 
Bromus 3 sps., Alopecurus 1 sp. 


Puccinia 





+ 


tr 


tr 


tr 


+ 


Ave?ia 2 sps., Agrostis 3 sps., 


graminis 














Anthoxanthum 1 sp., Dactylis 1 


avence 














sp., Kloeeria 1 sp., Panicularia 1 
sp., Arrhenatherum 1 sp., Alope- 
curus 2 sps., Bromus 3 sps., Cala- 
magrostis 1 sp., Holcus 1 sp., 
Phalaris 1 sp., Agropyron 1 sp., 
Beckmannia 1 sp., Elymus 2 sps., 
Festuca 2 sps., Hordeum 3 sps., 
Hystrix 1 sp., Lolium 3 sps., 
Phleum 1 sp., Secale cereale. 



278 



Diseases of Economic Plants 





Q 






55 


?5 


S3 


Also on other genera of grasses 







-2 




'S 
c 






as below 




O 
tr 


Qq 


05 
tr 


+ 







Puccinia 


tr 


Dactylis 1 sp., Festuca 2 sps., 


graviinis 














Koelerixi 1 sp., Phleum 1 sp., Alo- 


phleipra- 














pecurus 2 sps., Holcus 1 sp., 


tensis 














Avena 2 sps., Arrhenatherum 1 sp., 
Bromus 1 sp., Elymus 1 sp., Hor- 
deum 2 sps., Lolium 2 sps., Secale 
cereale. 


Puccinia 





tr 


tr 


tr 





+ 


Agrostis 3 sps., Alopecurus 2 


graminis 














sps., Bromus 1 sp., Dactylis 1 sp.. 


agrostis 














Holcus 1 sp., Koderia 1 sp., Avena, 
1 sp., Calamagrostis 1 sp., Hor- 
deum 1 sp., Secale 1 sp. 


Puccinia 














Aira ccespitosa, A. hottnica. 


graminis 
















airce 
















Puccinia 














Poa compressa, P. ccesia, P. pra- 


graminis 














tensis. 


poa 
















Puccinia 


+ 





tr 


+ 





+ 


Agropyron 7 sps., Elymus 4 sps., 


graminis 














Hordeum 2 sps., Triticum 7 sps.. 


tritici- 














Bromus 1 sp., Secale 1 sp. 


compacti 
















Puccinia 








+ 








simplex 
















Puccinia 




+ 




tr 


+ 





Alopecurus 1 sp., Anthoxanthum 


coronata 














1 sp., Avena 1 sp., Dactylis 1 sp., 
Elymus 1 sp., Hordeum several 
species. 


Puccinia 






tr 










dispersa 
















Puccinia 






tr 








Sorghum vulgare, and *9. holo- 


purpurea 














penses. 


Puccinia 


+ 














triticina 
















Puccinia 


+ 




+ 


+ 








glumarum 

















+ =host 



0=no infection tr=rust infects weakly 



Cereals 279 

All cereal rusts multiply much more rapidly in damp 
than in dry weather, and are more destructive to late crops. 
There is no evidence that these maladies can be carried by 
seed from rusted plants, though such seeds should not be 
used for seed purposes, since they do not have stored nourish- 
ment sufficient to give the seedling a vigorous start. 

Great difference in rust resistance has been shown; thus 
while one variety of grain was so badly affected as to yield 
only 23^ bushels per acre, a resistant variety under the same 
conditions gave 383^ bushels. 

The greatest hope lies in the use of varieties which can 
resist the disease. A number of different kinds of grain are 
now known which possess sufficient resistance to give good 
yields even when the rust is in its worst form. Since serious 
outbreaks of rust must be looked forward to with certainty, 
the item of rust resistance must have due weight in the selec- 
tion of the variety to be grown. 

Several varieties of oats of the red group, among them 
the Burt, Appier, and Cook when grown in the Southern 
States, are known to possess valuable resistance to the oat 
rust. Similarly there is large difference betvv^een varieties of 
wheat as to rust susceptibility. 

Early maturity in oats is of especial value in that it enables 
the plant to evade the heaviest part of the rust attack. Good 
drainage and clean culture conduce to plants of more 
resistance to rust, as does also good preparation of the seed 
bed. Drilled wheat is better lighted and better ventilated and 
resists rust more effectively than wheat that is broadcast. 

Wild grasses that harbor rusts identical with the rusts 
of crop plants, such as wild meadow oat grass, orchard 
grass, wild wheat grasses, quack grass, wild rye grasses, 
etc., may propagate the fungus and increase infection. If 
such grasses are rusted, they should be burned, plowed 
under, or avoided in the location of the grain fields. 

While sprays of various kinds may be effective in checking 
the spread of rusts, the use of such means of prevention is 
impracticable, owing to the nature of growth of the crop, 



280 Diseases of Economic Plants 

and the difficulty and expense of the application. Moreover 
the question of use of such treatment is complicated by the 
different kinds of rusts to be met and by their different 
behavior in different seasons. 

Anthracnose of Cereals 

Anthracnose ^^^ {Colletotrichum cereale Manns) . — Upon 
many cereals and forage crops, as rye, wheat, oats, orchard 
grass, timothy, red-top, and blue-grass, occurs a blight, 
resulting in shriveling of the grain and spotting of the leaves 
and stalks. The fungus is marked by small, black acervuli, 
located upon the spikes, stems, and sheaths. The chief at- 
tack is made as the plants approach maturity. 

For further discussion, see rye. 

Special Diseases of Cereals 
BARLEY. 

Loose-smut ^^^ {Ustilago nuda (Jens.) K. & S.). — This 
disease, previously thought insignificant, seems to be in- 
creasing in importance. It now often causes losses in Wis- 
consin and Minnesota of from 5 to 10 per cent of the crop, 
and is generally prevalent in this country, though often 
unnoticed on account of the early season of its development, 
and its absence at harvest time. Every spikelet of the 
smutted head is usually affected and entirely changed into 
smut, the central stalk of the head alone escaping. Adjacent 
leaves are also occasionally smutted. 

The smut masses, when they first appear, are covered by a 
white or gray membrane which soon ruptures, loosing a 
powdery, olive-brown mass of spores, which soon blow 
away. This character enables one to distinguish it easily 
from the covered smut. Smutted plants head early, the 
smut reaching its maximum at flowering time, though 
scattered heads of smut may appear at other periods. The 
smutted heads stand high on tall stalks, which affords ex- 
cellent wind distribution of the spores to the surrounding 



Cereals 



281 



blossoms. The fungus, reaching the blossoms, gains such 
foothold upon the developing grain that its use as seed, with- 
out treatment, insures a smutted seedling as offspring. In 




Fig. 147. — Loose-smut of barley in various stages of development. 

After Johnson. 

the plant developing from such an infected seedling the 
disease does not show externally until the smut ripens at the 
next blossoming season. 

The life history of this smut is thus similar to that of 



282 Diseases of Economic Plants 

wheat loose-smut, and the same treatment, i. e., rogueing, 
combined with a modified Jensen hot-water treatment, is 
effective. See p. 272. 

Covered-smut^-'' (Ustilago hordei (Pers.) K. & S.). — ■ 
In the covered-smut, the smut masses replacing the grains 
and glumes are at first covered by a membrane composed of 
the outer surface of the glumes of the spikelet. This mem- 
brane retains the spores for some time after harvest. The 
spores, as seen en masse, after the rupture of this cover are 
very dark to purplish black, with no tint of olive. 

The formalin treatment applies here. 

Ergot. See rye. 

Black-stem-rust (Puccinia graminis Pers.). — The forms oc- 
curring on both wheat and rye develop equally well on barley, 
and severe attacks of either form are common. See wheat. 

Dwarf -leaf -rust (Puccinia simplex (Koern.) E. & H.). — 
Reported from Iowa in 1896, later from California, Minne- 
sota, Virginia, Wisconsin, Wyoming, and Maryland, this rust 
seems to be of recent introduction and generally of minor 
importance, though serious in the extreme West. 

Blight ^^^ (Pseudomonas translucens J. J. & R.). — Water- 
soaked areas appear on the leaves extending in longitudinal 
stripes or blotches between the veins. Later they turn brown. 
Small, gray drops of exudate appear on either leaf surface. 
Distortion of the head may be caused by disease of the en- 
veloping leaf. It has been observed in nine states from 
Ohio to Oregon, on many varieties of barley. Infection ap- 
pears to be by means of the seed. 

Stripe-disease (Pleospora gramineum Diet., Helmintho- 
sporium) . — This leaf blight was discovered in America 
by Pammel in 1890. It is characterized by longitudinal, 
yellowish-green spots in parallel rows upon the leaves. The 
plants die prematurely, and the yield is thus reduced. It is 
reported from many states. The loss in some fields amounts 
to from 10 to 50 per cent of the crop. Stripe is almost en- 
tirely prevented by formalin seed treatment (1 pt. to 30 gals., 
2 hrs.). 



Cereals 283 

Net-blotch ^^' {Helminthosporium teres Sacc). — First 
known in the United States in 1907, this disease has been 
observed in Iowa, South Dakota, Minnesota, and Sas- 
katchewan. It occurs as brownish, circular, or somewhat 
elongated dark spots which soon cause the leaves to turn 
brown. It also occurs upon sheaths, glumes, spikelets, and 
grain. The straw at harvest is dull brown and lacks strength. 

Scab, Powdery-mildew, Yellow-stripe-rust. See wheat. 

BROOM CORN 

Kernel-smut ^^^ {Sphacelotheca sorghi (Link) Clinton). — 
Irregular, elongated branches of inferior value indicate the 
presence of the smut. The branches are further damaged by 
blackening occasioned by the loose spores. The seeds are 
destroyed. Of the fields examined by Clinton in Illinois few 
showed over 1 per cent of the stalks infected, though some- 
times parts of a field })ore as high as 20 per cent of diseased 
stalks. Infection can occur only upon very young plants. 
Between the times of infection and the appearance of the 
smut masses in the panicle no signs of the disease are seen 
without the aid of the microscope. 

The smut can be prevented by the use of clean seed, 
obtained either from clean fields or by disinfecting the 
seed by the hot water (58° C. (135° F.) for 10 to 15 minutes) 
or formalin methods. 

CORN, TEOSINTE 

Smut^^^ (Ustilago zeoe (Beckm.) Ung.). — Corn smut is 
well known to every farmer, occurring wherever the corn 
plant is grown, as black, pulverulent masses most conspicuous 
upon the ear and tassel. The damage in 1917 is estimated at 
108,000,000 bushels. In Iowa a loss of two-thirds of the crop 
was at one time reported. 

Corn smut is first mentioned in literature in 1754, and 
the first record of it in America is in North Carolina in 
1822, Experiments looking to its prevention were made 



284 



Diseases of Economic Plants 



as early as 1760. The disease may attack any part of the 
plant at any age, — leaves, stalks, aerial roots, ears, tas- 
sels, — provided only that they be still in tender growing 
condition, not mature and hard. 

The first symptom 
is a pale, glistening, 
swollen area covered 
with a white mem- 
brane, which soon ap- 
pears black owing to 
matured spores 
within. The mem- 
brane eventually 
bursts, loosening a 
powdery, dry, black 
mass of spores 
through which fibrous 
veins of the corn 
plant still penetrate. 
It has been conclu- 
sively demonstrated 
that the causal fungus 
is not conveyed to 
the new crop in the 
seed, as is the case 
with so many other 
smuts, and that there- 
fore no form of seed 
treatment is of value 
for its prevention. 

It has been clearly 
shown that infection 
is produced by the 
spores which, under 
suitable conditions of moisture, fall upon any tender part of 
the corn plant. The silks furnish the requisite conditions, 
and it is through them that ear infection occurs. The 




Fig. 148. 



Corn smut upon the ear. 
Original. 



Cereals 



285 



sheaths of the leaves hold water, and inclosing as they do 
the tender growing portion of the stem, are admirably suited 
to infection. Since infection cannot occur without moisture, 
weather conditions are of predominating influence. 




Fig. 149. — Smut upon sweet corn tassels. After Jackson. 

The longer the crop grows, the longer the period of sus- 
ceptibility is maintained. Thus a late-planted crop in In- 
diana showed half as much infection as a crop which was 



286 Diseases of Economic Plants 

planted earlier, chiefly -because it was exposed to contagion 
only about half as long. Moisture and richness of soil 
predispose to disease by increasing growth and giving a 
greater number of susceptible points of attack. Corn thickly 
planted is more liable to infection because ventilation is 
restricted, and thus a more humid atmosphere is maintained 
around the plants. 

It has been shown that corn smut can be reduced by 
spraying with Bordeaux mixture, but the saving does not 
warrant the expense. To go through the field several times 
during the season and cut out and burn all the developing 
smut masses that can be seen, thus to destroy the spores and 
prevent the continued spread of the disease, is recommended, 
but the actual utility of such practice has not been demon- 
strated, though it is probable that this practice continued 
yearly would result in continued diminution of smut. The 
use of the silo in which the smut spores are rendered non- 
viable tends to lessen the amount of smut. The smut fungus 
can live and even increase in manure. Therefore live smut 
spores may infest the manure pile and thereby increase the 
disease in fields to which such manure is applied. The smut 
itself, contrary to popular belief, is poisonous to stock only 
under very rare and exceptional conditions, so rare as to be 
practically negligible. Fresh smut balls that have not yet 
turned dark are edible, and, prepared as mushrooms, are 
delicious. 

Head-smut (Sphacelotheca reiliana (Kuehn.) Clint.). — 
This smut, identical with that of sorghum, occasionally 
occurs upon corn and is somewhat more injurious though less 
common than the usual corn smut. It cannot be controlled 
by seed treatment. 

Corn Ear Rots ^^^ 

Four types of ear rot, due to four distinct diseases, are 
described below. In the aggregate the loss from these is 
enormous, constituting as it does 10 per cent or more of a 
crop annually. Infection comes from definite species of 



Cereals 



287 



fungi, and is not comparable to ordinary 
molding of dead organic matter by fungi 
of varying kind. 

Dry-rot {Diplodia zece (Schw.) Lev. 
and Diplodia macrospora Earle) . — This 
is one of the very widespread, dry ear 
rots of corn variously known to growers 
as mold, mildew, rot, dry-rot, etc. 

Though the disease is really present 
soon after silking, and even much earlier 
from root infection, it is not usually 
recognized until husking, when a whitish 
covering of the kernels within the husk 
is noted. This white mycelium also 
forms dense masses between the indi- 
vidual grains, among the husks, and over 
the cob. The grains on the affected ear 
are shrunken, loosely attached, light in 
weight, darker in color, and more brittle 
than those of a healthy ear. Upon 
breaking open an ear, very small black 
pycnidia may be seen embedded in the 
white masses of mycelium, especially at 
the bases of the kernels. Diseased ears 
left in the field may develop these pycni- 
dia in such abundance as to make the 
grains black. 

Much of the food value of the corn is 
lost, owing to the consumption of starch 
within the grain, as well as to the pre- 
vention of starch storage. The germi- 
nating power of the grain is also lost. 

Upon the stalks the fungus first 
appears as very small dark specks under 
the rind, near the nodes, and at broken 
places, usually in over-wintered stalks. 
Three-year-old stalks have been found 





Fig. 150. — Young 
ear of com inocu- 
lated in the silk 
with Diplodia. Af- 
ter Burrill and 
Barrett. 

bearing pycnidia. 



288 



Diseases of Economic Plants 



Although the green stalks are not naturally susceptible, 
the shanks are particularly so. 

The causal fungus gains entrance to the ears from attacked 
stalks which bear them, and these are in turn infected 




Fig. 151. — Diplodia on old shanks. After 
Burrill and Barrett. 

through the roots from the soil. Ears are also invaded 
through the silks by wind-borne spores, which come, in part, 
from diseased ears, but more largely from diseased stalks 
left in the field. 



Cereals 



289 



Any method of reducing the 
amount of infective trash, par- 
ticularly old stalks near or in the 
fields, aids in control of this pest. 
Practically, this means to take 
out of the field and destroy all 
rot-infected ears and to cut in- 
fected stalks low and haul them 
away or burn them. It is still 
better to practice such rotation 
that corn will not follow corn 
within two years. 

Dry-rot (Fusarium sps). — 
Upon the ears this disease ap- 
pears as a dense, felted, white 
mycelium, extending between 
the kernels to the cob. The 
kernels are killed and their 
starch partly consumed. 

A second Fusarium disease is 
characterized by a deep pink 
to red color noted on the ear 
when the husks are removed. 
The kernels are brittle and 
the starchy portion within is 
powdery. 

A third Fusarium disease 
causes less complete destruction 
of the ear than the preceding; 
often only a few scattered ker- 
nels are affected. The mycelium 
is white and sparse. A cob- 
rot ^^^ due to Coniosporium 
softens the cob without mate- 
rially injuring the grain. 

Root-rot, stalk-rot =^1^' ^0^' ^0^' ^-^ (Fusarium sps.). — The 
first record of root and stalk-rots of corn was made in 1907 by 




Fig. 152. — Corn mold caused 
by Fusarium. After Burrill 
and Barrett. 



290 



Diseases of Economic Plants 



Selby, in Ohio. In 1914, Pammel, in Iowa, called attention 
to a serious root-rot of corn caused by a Fusarium. The 
disease is now known to prevail generally throughout the 
corn belt both in the South and the North. Though no ac- 




FiG. 153. — Rotten stalk and the nubbin re- 
sulting. After Hoffer. 

curate estimate has been made of the amount of damage, it 
is known that the loss is large. 

Among the symptoms are: 1. Poor stands due to missing 
hills, caused by defective germination. 2. Weak and stunted 
seedlings, many of which may eventually die. Stunted 



Cereals 291 

plants show decayed roots and purplish-brown discolored 
stalks when split lengthwise. 3. Down-stalks due to rotting 
of the roots, so that the plant falls over. 4. Broken stalks 
due to weakening, chiefly at the nodes. 5. Barrenness and 
nubbin formation. The infected plant lacks vitality to form 
a perfect ear. 6. Broken shanks due to rot. 7. Diseased 
kernels. The kernels may be molded and cracked, though 
no sign of disease may be apparent and the infection or 
weakening of the kernels shows only on germination. The 
severity of the attack depends upon the stage of develop- 
ment, the vigor and resisting power of the corn plant as 
determined by the conditions for growth and development, 
and by its heredity. 

Root-rot is caused by fungi, mainly Fusarium, and arises 
chiefly from primary infection, from infected seed, though to 
some extent from secondary infection in the field. The 
planting of infected seed is largely responsible for missing 
hills, down-stalks, nubbins, and other signs of disease. 

No infected corn should be used for seed. To eliminate the 
infected seed, special adaptation and care in using the rag- 
doll tester, or the use of special testers, devised by Hoffer, is 
necessary, whereby the seedlings that show infection, when 
less than three inches in height, may be recognized and the 
ears from which they originated discarded. 

Since the wheat scab organism (Giberella) causes rot of 
stem and shank of corn, corn so diseased increases the amount 
of wheat scab in succeeding crops. 

Wilt ^^^' ^^^ {Pseudomonas stewarti EFS.). — This corn wilt 
was first described by Stewart as prevalent in nearly all parts 
of Long Island upon many different varieties of sweet corn. 
In some cases the entire crop was ruined, and 20 to 40 per 
cent of loss was frequent, though in the majority of cases the 
loss was so slight as to pass without notice. It has been 
noted on sweet corn in Kentucky and Illinois, but rarely on 
field corn. 

The diseased plants wilt and dry up much as though from 
lack of water, yet in soil that is amply supplied with water. 



292 Diseases of Economic Plants 

While the wilting is most likely to occur at flowering time, 
it may appear at any stage of growth when the plants are 
25 cm. or more in height. In mild cases the lower leaves 
wilt first, while in severe cases all wilt at one time. The 
death of the plant may occur in four days after the first 
signs of disease, or may be delayed a month, possibly with 
recovery and relapse intervening. 

The roots remain normal, but the veins in the stems 
appear as yellow streaks, in older cases black, instead of 
their normal color. Such stems, if cut crosswise, shortly 
exude a yellow, viscid drop at the ends of the veins. This 
is the most distinctive character, and infallibly indicates 
the presence of the wilt. Death is caused by the plugging 
of the water passages with this viscid substance, which con- 
sists mainly of bacteria. 

In the fields the diseased plants, representing young and 
old stages of infection, grow side by side with normally 
healthy plants. Health and disease may appear, even in the 
same hill; yet there appears to be no direct plant-to-plant 
infection, nor any of that centrifugal spreading from a 
diseased center that is so noticeable in most wilt or soil-borne 
diseases. 

The causal organism is found in the seed from affected 
plants, and it has been proved experimentally that such 
seed carries the disease to the offspring. 

As a preventive measure resistant varieties should be 
selected for planting, and all seed from plants which are at all 
diseased should be avoided. The disease may be carried from 
one locality to another by any of the means suggested under 
soil diseases, and especially by manure infested with stalks of 
diseased plants. 

Minor diseases 

Brown-spot ^^^ (Physoderma zece-maydis Shaw) was first 
noted in India in 1910, in Illinois in 1911. Its distribution 
is shown in the accompanying map. (Fig. 154.) Considerable 
damage is done in the region indicated by the darker shading, 



Cereals 



293 



but it is hardly probable that this disease will extend seriously 
or become very destructive, except locally, and in very 
humid, hot seasons. In some cases, the injury is as high as 
6 to 10 per cent of the crop. The fungus grows in leaf, 
sheath, and stem, rarely in the husks. Bleached or yellow 
spots about 1 mm. in diameter first appear, and within a few 
days darken, eventually becoming reddish-brown. Coales- 




FiG. 154. — Map showing the distribution of Physo- 
derma zea3-maydis in the United States. Broken hnes, 
P. zeae-maydis present: solid line, P. zeae-maydis caus- 
ing damage. After Tisdale. 

cence of many spots may lead to discoloration of large areas 
and a rusted appearance. These diseased areas are often in 
bands across the leaf. Leaves are often killed. The dry 
epidermis eventually ruptures over diseased spots and the 
dusty, brown spores are freed. Diseased stems break easily, 
resulting in considerable lodging of the corn. General san- 
itary measures are recommended, chiefly destruction of in- 
fested refuse and rotation of crops. 



294 



Diseases of Economic Plants 



Blight ^^'^ (Pseudomonas sp.). — This disease was described 
by Burrill in 1889. 

It shows chiefly as a dwarfed condition which may occur 
in spots in the field, varying in size from a few square rods 

to an acre or more. The 
affected plants finally turn 
yellow, and most of them 
die. 

The lowest roots of dis- 
eased plants, in some cases 
comprising half of the root 
system, die. The stalk 
near the base, when split 
lengthwise, shows a uni- 
form, dark color which 
also appears in the upper 
nodes in lesser degree. 

Rust (Puccinia sorghi 
Schw.) . — Corn rust seems 
to have taken its place in 
literature in 1815. It is 
comparatively of slight 
importance, since it does 
not usually develop early 
in the season, though 
in exceptionally favorable 
climatic conditions it may 
do so. The brown sum- 
mer spores appear first in 
linear sori, and the black 
winter spores come later 
in the season. The cluster- 
cup stage is found upon 
the wood sorrel (Oxalis). 
Yellow-leaf ^^^' ^^^ (Helminthosporiurn inconspicuum C. 
& E.). — This blight gives a somewhat frostbitten ap- 
pearance to the plants, producing also a thin olive-green 




Fig. 155. — Portion of corn leaf show 
ing sori of rust. 



Cereals 295 

mold upon the lower sides of the leaves. Sometimes only the 
tips of the leaves are affected, but usually whole leaves die. 

Yellowish, elongated spots limited by the veins, sometimes 
covered with dark-colored spores, are produced. The disease 
is confined almost entirely to late-planted corn, and is 
prevalent during its early growth, though it has never been 
reported upon seedlings. 

It is known to cause much loss in Delaware, New York, 
and Connecticut, and is of widespread occurrence in the 
United States. 

Chlorosis appears to be related to the mosaics in that it is 
transmitted by sap or by contact. It occurs also in the 
embryo. Two species of Sclerospora cause considerable 
injury to corn in Italy, and have been collected in the United 
States. The tassel is chiefly affected. Phyllachora causes 
damage to corn in the warmer climates. In the Orient very 
great loss is caused by a downy-mildew (Peronospora) . 

EMMER, EINKORN. See p. 310. 

KAFIR. See p. 307. 

MILLET 

Leaf-spot ^"^ (Piricularia grisea (Cke.) Sacc). — Upon the 
lower leaves the disease occurs as a spot which is at first dark 
purple or reddish, and elongated parallel with the length of 
the leaf. Later the center turns black and finally straw- 
colored, bordered by a black ring which merges into reddish- 
purple at its outer edge. Badly diseased leaves turn yellow, 
dry and shrivel from the tip toward the base, lessening the 
fodder value and seed yield of the plant. 

Smut {Ustilago crameri Koern.). — This smut infects the 
individual flowers of the fox-tail millets, destroying the lower 
parts of the glumes and the grain. It has been noted in Ohio, 
Minnesota, Connecticut, Illinois, Indiana, Iowa, Maine, 
Michigan, Colorado, North Dakota, and South Dakota. 
U. panici-miliacei similarly affects the Panicum millets. 



296 



Diseases of Economic Plants 



The formalin treatment, 1 pint to 40 gallons, is applicable 
to both of these smuts. 

MILO. See p. 307. 



OAT 

Loose-smut ^-'^' 2^3-345 (jjstilago avence (Pers.) Jens.). — 

Under the name "smut/' ''blackheads," etc., this disease is 

known wherever oats are 
grown. Grain and more 
or less of the chaff are 
replaced by a powdery, 
black mass, which shat- 
ters out as it ripens, leav- 
ing later only the naked 
branches of the panicle. 
Usually all the spike- 
lets of a head and all 
the heads of the affected 
plant are smutted. 
There is considerable dif- 
ference in the resistance 
offered by different va- 
rieties, but in view of the 
perfect protection af- 
forded by proper treat- 
ment this is of little 
significance. 

The damage caused by 
smut is commonly under- 
rated. In 1884 Arthur 
in New York by actual 
count found the oat 
smut to constitute from 
8.5 to 10 per cent of the 

Fig. 156. — Loose smut on oats. After ordinary crop. By ac- 
Jackson. tual count of nearly 




Cereals 297 

11,000 heads Plumb in 1886 determined the amount of smut 
to be 8.4 per cent; in some fields he found as high as 20, 28, 
and even 30 per cent. Kellerman and Swingle, counting 
smutted heads in Kansas, found different fields to have 8, 
15.3, and 18.3 per cent of smut, while single portions of a 
field showed as high as 30 per cent. The loss in this country 
in 1917 was estimated as approximately 91,000,000 bushels. 

The reasons for underestimation of oat smut are: 1, the 
dwarfing of many of the affected plants, which thus re- 
main unnoticed by a casual glance over the field; 2, the 
fact that many smutted panicles remain invisible unless 
unrolled from their enveloping leaves. 

It was proved as early as 1858 that infection can occur 
only upon the very young oat plant; that older plants are 
immune. It was later determined by Brefeld that the 
plants are immune after the leaves have protruded 1 cm. 
beyond the leaf sheath. From this and other experiments 
it follows that practically all infection comes from smut 
spores which are upon the seeds when they are planted. 
These germinate, producing sporidia which infect the young 
plant. The fungus develops in these plants throughout the 
season without conspicuous effect until, at blossoming time, 
the fungus seeks the ovaries and the glumes and appears 
again as the familiar black spore masses. 

Any treatment which kills the spores upon the seed with- 
out materially injuring the seed itself results in a clean crop. 

The copper sulfate treatment endangers germination of 
oats. The hot water treatment is less convenient than the 
formalin treatments which are thoroughly satisfactory. 
See p. 270. 

Covered-smut (Ustilago levis (K. & S.) Magn.). — This 
differs from the loose smut in the less complete destruction of 
the flowers and in its less dusty spore masses, which are also 
blacker than in the loose smut. The smut masses are usually 
limited to the parts within the flowering glume and the palet 
or to the bases of these. 

The treatment is that given for loose smut. 



298 



Diseases of Economic Plants 



Black-stem-rust (Puccinia graminis avence E. & H.). — 
The black-stem-rust on oats shows but slight differences from 
the black-stem-rust of wheat, but it is racially 
distinct (see p. 277) and a field of one of these 
crops may be badly affected by its fungus, 
while adjacent fields of the other crop show 
no rust or indication of infection such as they 
might be supposed to do were the two rusts 
identical. 

As with the wheat black-stem-rust, its at- 
tacks fluctuate greatly in abundance and 
destructiveness from year to year. 

Crown-rust (Puccinia coronata Cda.). — 
This rust is found only upon species of oats 
and closely related grasses and in the telial 
stage clearly differs, even to the naked eye, 
from the oat rust mentioned above. 

It occurs upon oats in practically all fields 
but is more injurious in its southern range. 
The damage is not serious, or very rarely so. 

The cluster-cup stage is known to grow 
upon the common buckthorn (Rhamnus cath- 
artica) and the lance-leaved buckthorn {R. 
lanceolatus) . The yellow uredinial stage is 
most conspicuous. Later the black telia ap- 
pear under the epidermis as long streaks 
which, unlike most rusts, do not rupture the 
epidermis. 

Marked varietal resistance is shown. In 
California black oats are reputed to be less 
subject to rust than white oats. In the 
North, the White Russian is said to be resist- 
ant, while in the South, the red oats resist 
attack. 
Minor diseases 

Scab. See wheat. Leaf-spot (Phyllosticta sp.). — Browned 
or reddened leaves, with the black pycnidia profuse upon the 



Fig. 157.— Cov- 
ered-smut on 
oats. After 
Jackson. 



Cereals 299 

affected surfaces, sometimes so abundant as to lend a blackish 
hue to the leaf, comprise the diagnostic symptoms of this 
malady. Eventually the leaves are killed. 

Blight ^^^' ^^^ (Pseudomonas avence Manns) . — A disease 
prevalent throughout the Eastern and Central States was 
attributed to bacteria by Galloway and South worth in 1890. 
It appears when the plants are only about 10 cm. high, first 
causing the leaves to turn brown and die at the tips, then 
throughout their length. The affected plants revive, but 
are so reduced in vigor as to prevent effective stooling, and 
a loss of from 35 to 75 per cent of the crop commonly 
occurs. 

The disease was carefully investigated by Manns, who 
claims that it is caused by the symbiotic action of two species 
of bacteria, a Pseudomonas and a Bacillus. 

Manns describes the disease as follows: 

The preliminary effect is yellowing of the leaf, beginning 
either as small, round lesions on the blade, or as long, streak- 
like lesions extending throughout the blade and even the 
whole length of the culm and blades. Occasionally it begins 
at the tips and works back into the culm; again the upper 
leaves often break down due to a weakened condition of 
the plant from defoliation below. 

The ultimate symptoms, wherever the disease has made 
much progress, are partial or general collapse of the leaves, 
which take on a mottled to almost red color. 

It prevails from New England to Georgia, and from the 
Atlantic to Indiana and Illinois. The damage in Ohio has 
been estimated at from 14 to 37 per cent of the crop. Rain 
and moisture favor it. 

When prevalent, the soil may become infested as in typical 
soil diseases. The only hope seems to rest in resistant 
strains. 

Halo-blight (Bacteria). — Oval, chlorotic areas 1-2 cm. in 
diameter, bordering a minute, sunken, dead center, occur 
in the leaf. Stripe-blight (Bacteria). — The diseased tissues 
are water-soaked, translucent, with an abundant exudate and 



300 Diseases of Economic Plants 

no halo. The spot is long and narrow, between the veins. 
Anthracnose (Colletotrichum cereale) . — The effect of this 
disease upon oats is similar to that described for rye. Yellow- 
leaf {Hebninthosporium inconspicuum C. & E. var. hrittani- 
cum Grove) . — Oat leaves turn yellow and develop dark, 
brown, spore-bearing spots. Little is known as to its severity 
or prevention. Powdery-mildew. See wheat. Ergot occurs 
but rarely on oats. 



RICE 



348 



Blast, rotten-neck ^''^ {Piricularia cry zee Cav.). — This is a 
world-wide rice disease, which in Italy is controlled by the 
use of resistant varieties. It has probably been present 
for many years in American rice sections, but did not become 
of serious economic importance until about 1895. What 
seems to be the same disease occurs upon crab grass, and 
apparently infection may come from this host. It is reported 
from South Carolina and Louisiana, also from Texas, where 
it has been serious. The disease occurs upon upland as well 
as irrigated fields. 

The most characteristic symptom consists of lesions at 
the sheath nodes just over the joints of the stem, at the 
region where the stem comes to be the axis of the head 
(the ''neck region") and at the points where the blades of 
the leaves join their sheaths, appearing first as very small, 
water-soaked, sunken spots on the node of the sheath. Spots 
upon the neck are not water-soaked, and the skin does not 
rupture until the head breaks off. Later the spot becomes 
brownish or black, and similar discoloration runs upward and 
downward. The affected stem tissue gradually extends 
laterally, shrinks, and dies, cutting into or through the joint, 
which results in an open wound. The region above the 
wound becomes pale and dies. 

Upon young plants leaf spots occur, first brown with ashen 
center, later coalescing and taking the whole leaf. If the 
attack is early, the grain does not fill at all; if late, it may 



Cereals 



301 



partially fill. The dead portion of the plant may bleach or 
darken according to environment, resulting in varied char- 
acters in later stages of the disease. In 70 per cent of 
the cases examined by Metcalf the lowest 
joint of the rachis was affected, and in 
consequence the heads broke off at this 
point. This gives rise to the common 
name ''rotten-neck," but since the char- 
acter is not universal, the name is not an 
appropriate one. 

The chief damage results from the failure 
of the grain to fill on the diseased stalks. 
An early attack may render a crop entirely 
worthless. Plants attacked later, yield 
some grains which are of poor, light qual- 
ity, easily broken or blown away, and con- 
sequently largely lost in threshing and 
milling. The variation in size of the grain 
also largely depreciates the quality. Many 
of the heads, especially the heavier ones, 
fall off, and some fields show at least 
one-third of the crop thus left upon the 
ground. 

The Rice Committee of the Agricultural 
Society in South Carolina, March, 1904, 
estimated the loss, up to that time, to be 
very nearly $1,000,000. Depreciation in 
land values, necessitating abandonment of 
land, is a significant item of charge against 
this disease. 

The chief hope hes in the use of resistant 
varieties. Withholding nitrogenous ferti- 
lizers and removal of infective trash by 
burning are good sanitary measures. 

Green-smut {Ustilaginoidea virens (Cke.) Tak.). — This 
grain disease, though partaking of the appearance of a true 
smut, is in reality more closely related to the ergot of rye. 



Fig. 158. — Rice 
blast. After 
Fulton. 



302 



Diseases of Economic Plants 



The grains, usually only a few in each head, become en- 
larged, spherical, 5 mm. or more thick, and coated with 

a dark green powder. Some- 
times a yellow color prevails 
instead of the green. In sec- 
tion the interior is seen to be 
filled with a compact white 
mass bordered by a brownish 
yellow zone, then by the green 
coating. 

Though the disease has been 
known in Louisiana for ten or 




Fig. 159. — Rice showing 
"green-smut." After Fulton. 

more years, and is present to 
some extent in most fields, it is 
not considered serious, since 
rarely more than 0.25 per cent 
of the heads, and only a few 
grains per head, are affected. 

Black-smut ^''^ (Tilletia horrida 
Tak.). — A dark, unsalable flour, 
made from rice in the region of 
Georgetown, S. C, was reported 
in 1898. Anderson found that 
many heads of rice from these 
fields bore as much as 25 per 
cent of smutted grains. 

This smut was probably imported from Japan in infected 
seed, but due to the immediate action of Anderson and 
Walker the pest seems to have been completely stamped 




Fig. 160. — Rice showing 
black-smut. After Fulton. 



Cereals 



303 



out in South Carolina within the first few years after its 
advent. No reports whatever of its presence there have 
been made since 1903. It has since entered the United States 
through Louisiana. 

The smut closely resembles the stinking smut of wheat. 
The affected ovaries or grains are transformed into smut 
masses which remain within the glumes, and so resemble the 
normal grains as often to be mistaken for them. The fungous 
mycelium grows within the stem tissue of the diseased plant 
and, as is the case with wheat bunt, infection probably 
occurs in the seedling stage, the fungus remaining unnoticed 





Fig. 161. — Three rice spikelets: A, normal; 
B, smutted; C, glumes partly torn away ex- 
posing the spore mass. After Anderson. 

until its presence in place of the grain is disclosed as a black 
spore mass. 

The disease can be controlled by the method which 
stamped it out in South Carolina; that is, by the formalin 
treatment. 

Damping-off. — Two forms of damping-off of seedlings 
are known: 

1. Rice, not covered, but simply flooded with water, 
frequently shows soft rot of the shoot in very young 
seedlings. 

2. Covered rice often shows damping-off spots just above 
the surface of the ground. 



304 Diseases of Economic Plants 

The causes of these rots have not been fully studied, but 
they are probably due to fungi or bacteria or both. 

Minor diseases 

Spotted-blight (Macrosporium sp.). — Small black spots 
of mold upon poorly filled grains sometimes occur, occasion- 
ally affecting field areas of considerable size. 

Speck, pip (Saprophytic fungi and bacteria). — The grain 
in some instances bears one or more discolored, often sunken, 
circular areas, 1-3 mm. in diameter, bounded by dark mar- 
gins with gray or pale-buff centers and often with a minute 
dark spot in the very center. In other cases the grain is 
shriveled and distorted without any definite spot. The 
interiors of the grains are chalky and brittle, and of such 
inferior quality as to be largely depreciated in value. Not 
infrequently from 10 to 25 per cent of the grain is affected, 
and in some cases nearly 100 per cent. The germinating 
power is much reduced. 

The disease is caused by the invasion of saprophytic fungi 
or bacteria into wounds caused by sucking bugs. Methods to 
control these insects have not been thoroughly worked out. 

Rust (Physiological) . — The leaves die gradually, begin- 
ning with the tips of the lower ones. Red spots and streaks 
usually appear before the leaves lose their green color. The 
roots are poorly developed, the plants dwarfed, and the heads 
small and light. 

RYE 

Ergot (Claviceps purpurea (Fr.) TuL). — Ergot is widely 
known as a black or purplish body, several times larger 
than the seed of the affected plant, which displaces the 
ovary or grain. Ergot occurs commonly upon rye and 
many other species of grass, as wheat-grass, wild ryes, blue- 
joint, Kentucky blue-grass, Canada blue-grass, red-top, 
timothy, and rye-grass. Of the last named, one farmer 
reports 1000 tons of hay so badly affected as to be worthless. 
Ergot is occasionally injurious on wheat. 



Cereals 305 

This disease is caused by the attack of a fungus upon the 
ovary while the plant is in bloom. The fungus invades 
and consumes the ovary and replaces it with the ergot, which 
consists of a dense mass of tangled, interwoven mycelium, 
a sclerotium. Ergots, when mature and under suitable 
conditions, germinate, sending forth several stalks each, 
with club-shaped, knobbed tops. From these the spores 
issue to infect susceptible plants then in blossom. For 
some days the fungus spreads from blossom to blossom by 
means of other spores, and each infected ovary results in 
another ergot. 

Loss to the grain and the damage to the plant are slight. 
Chief injury from ergot arises from its effect upon cattle 
that are fed ergotized grain or graze upon badly infected 
grass. Animals become emaciated and rough-haired as the 
result of continuous feeding of ergot. Further symptoms of 
ergot poisoning are tardy circulation in the extremities, 
gangrenous sores upon the teats or mouth, and sloughing off 
of parts of the tail, ears, or hoofs. Abortion may also follow 
as an additional effect. 

Fields should be examined for the presence of ergot. If 
large quantities are found, the grass should not be used for 
hay or pasture. Ergot can be lessened by cutting susceptible 
grasses about flowering time, thus checking the spread of the 
fungus. Badly infested hay lands should be burned over to 
destroy sclerotia ; roadside grasses should be cut often enough 
to prevent the formation of ergot, and seed should be exam- 
ined to prevent the spread of ergot through this means. 
Seed may be freed of ergot by immersion in a 20 per cent 
solution of common salt, which will float the ergot to the 
surface. 

Black-stem-rust (Puccinia graminis secalis E. & H.). — 
The description given in connection with wheat applies 
here. 

Brown-leaf-rust (Puccinia dispersa E. & H.). — This 
rust bears a very close resemblance to the rust caused by 
Puccinia triticina upon wheat, but in careful inoculation ex- 



306 



Diseases of Economic Plants 



periments it has been impossi- 
ble to infect one of these hosts 
from the other. It is invari- 
ably present where rye is 
grown and is particularly 
abundant in the Southern 
States, though notwithstand- 
ing its universal presence it is 
not destructive. The uredi- 
nial mycelium remains alive 
in the South and continues to 
produce spores during winter 
in the leaf, as it probably 
does in colder climates as well. 
It is possible that it is in this 
way carried from season to 
season by volunteer rye in 
the fields. The cluster-cup 
stage occurs upon a member 
of the Borage family, but has 
never been found occurring 
naturally in America. 

Stem-smut ^-^' ^^^ (Urocystis 
occulta (Wallr.) Rab.). — Un- 
like many of the cereal smuts 
the stems and leaves as well 
as the floral parts are affected. 
It may be recognized by the 
usual, dusty, black spores, 
which occur especially at the 
joints. While this disease 
does not directly attack the 
grain, it does diminish the 
yield by weakening the plant. 
Loss from 25 to 40 per cent is 
reported in Minnesota, 60 per 
cent in Australia. Seedlings may be infected from spores 





\'^ 


\ 






|- 




\m 


m§/^ ' 




Am 


m 






1 




1 


Im 


k 




"^ 



Fig. 162. — Head of rye attacked 
by anthracnose. After Manns. 



Cereals 



307 



in the soil. When serious, the formaUn treatment combined 
with crop rotation should be employed. 

Anthracnose ^^^ {Colletotrichum cereale Manns) . — A serious 
disease of cereals and other grasses, chiefly rye, wheat, oats, 
timothy, blue-grass, red-top, and orchard grass, was dis- 
covered by Selby and Manns in 1908. 

It is a destructive pest of very general distribution, being 
found in all the fields examined in Ohio. In one field it is 
estimated to have reduced the yield from 75 to 25 bushels, 
and it is assigned as a prominent cause of shriveling, such 




Fig. 163. — Normal rye kernels and shriveled ones 
due to anthracnose. After Manns. 

as is often attributed to rust, as well as of whitening and 
blighting of plants preceding ripening. Parts of the head 
above the points of attack die. The portion of the head that 
is killed is a total loss, and the general decrease in vigor of 
the plant results in shriveled, light grains. Upon stalks and 
leaf sheaths, beginning at the ground and extending over 
several internodes, the acervuli may be so numerous as to 
cause blackening. 

No remedy is known. 

Powdery-mildew, Yellow-stripe-rust and Scab. See wheat. 

Stripe-disease and Stripe-blight. See barley. 

SORGHUM, SUDAN-GRASS, KAFIR, MILO 

Blight {Bacillus sorghi Burr.). — This blight was studied 
by Burrill in 1883 and described in 1887. It prevails upon 



308 Diseases of Economic Plants 

sorghum, broom corn, Kafir corn, and Milo maize, and 
has been noted in lUinois, Kentucky, Iowa, Louisiana, 
Ohio, Michigan, Nebraska, West Virginia, and District 
of Columbia, often in serious form. The chief character 
is irregular-shaped, elongated blotches of red, at first faint 
orange, upon the leaves and leaf sheaths, sometimes limited 
by the veins, and always more conspicuous on the inner 
than the outer sides. Smaller patches later blend, and the 
affected parts die and finally turn black. The lower sides of 
diseased spots upon the leaves often bear red incrustations, 
resulting from the dr3ang of the exudate from within. The 
roots show the same discoloration, and the outer parts of the 
rootlets die and become loose. If only slightly diseased, the 
plants may attain normal size. 

Badly diseased roots are evidenced by the yellowed tops 
and other signs of malnutrition. In advanced stages the 
roots give such poor anchorage that the plants may be easily 
pulled from the ground. 

Infected stalks should be burned and such rotation fol- 
lowed as to relieve the infested soil of susceptible crops for 
several years. 

Kernel-smuts ^^^ (Sphacelotheca sorghi (Lk.) CI., S. cruenta 
(Kuehn) Potter) . — These smuts infest the individual grains 
of the panicle, while the head as a whole remains nearly 
normal in appearance. The smutted grains are at first 
covered by a white, later gray, membrane. This membrane 
in time becomes broken by the winter exposure and frees the 
dark-colored spores. 

Kernel-smUt was reported by Kellerman in 1891 as limited 
to sorghum grown from imported seed. It was then known 
in the District of Columbia, Wisconsin, New York, Nebraska, 
and Kansas. It is widespread in Europe, Africa, and Asia, 
and was probably imported into the United States upon 
diseased seed. It was first recorded in the United States in 
1884, and is now found in almost all places where sorghum is 
grown. 

According to Clinton's estimates it may prevail upon 



Cereals 



309 



from 4 to 32 per cent of the plants. The same investigator 
found that the yield in juice was lessened about 30 per cent, 
owing to the smaller size of the smutted plants. The damage 
is particularly serious in kafir and broom corn. See p. 283. 

These smuts gain entrance to the host only during the 
very young seedling state, before the plants appear above 
ground. The mycelium of the causal fungus grows through 
the plant until flowering time without any indication of its 
presence. At blossoming time the fungus seeks the ovary, 
destroys it, and becomes evident as smut. 

Disinfection of the seed by formalin is an efficient remedy. 

Head-smut ^^^ (Sphacelotheca reiliana (Kuehn) Clinton). — 
Instead of involv- 
ing the grains 
singly, as in the 
kernel-smut, the 
head as a whole is 
affected. A white 
membrane is at 
first present, but 
this later breaks 
open, exposing the 
pulverulent spore 
mass. Rarely, only 
a portion of the head is smutted. The spores soon weather 
away, leaving behind only the veins of the part involved. 
This disease was first noted in Egypt in 1868, and is preva- 
lent in America only in the Texas Panhandle. It occurs on 
sorghum and to some extent on corn. Milo is immune. 

The only procedure to recommend is that employed for 
corn smut. 

Anthracnose (Colletotrichum falcatum Went.). — Anthrac- 
nose was first seen in America upon sorghum in North 
Carolina, where it did considerable damage. It has since 
been reported from Louisiana. The spots which are more 
prevalent on the lower leaves have very definite gray or tan- 
colored centers which are surrounded by dark, reddish- 




FiG. 164. — Three views ot sorghum kernel- 
smut. 



310 Diseases of Economic Plants 

brown rings, outside of which is the ordinary green of the 
healthy leaf. As the spots age they frequently grow together 
and form one large oblong area, sometimes several centi- 
meters long. At a late period in the development of the 
disease the centers of the spots are occupied by small black 
specks, the black acervuli of the causal fungus. 

TEOSINTE. See p. 283. 

WHEAT, SPELT, EMMER, EINKORN 

Black-stem-rust (Puccinia graminis Pers.). — Though in 
earlier years this rust was thought to grow indiscriminately 
upon a great variety of grasses, recent, thorough study has 
shown that what was formerly regarded as one species is in 
reality a number of races or va,rieties grouped under one 
name. Collected on about 70 species of wild and cultivated 
grasses including wheat, oats, rye, and barley, this rust is 
now separated into eight or more biologic forms. See p. 277. 

It is the most serious of the rusts, of practically world- 
wide distribution, and causes more damage in the Central 
States than any other rust except the oat black-stem-rust. 
It is injurious to oats, rye, and barley as well as wheat. The 
damage done fluctuates largely. The injury is greater to 
spring wheat than winter wheat. In 1916, the direct loss 
was placed at $110,000,000, in four states, 200,000,000 
bushels in the United States, and 100,000,000 more in 
Canada. Total loss of the crop often results in Kentucky, 
Indiana, Texas, Michigan, and Ohio. 

In the spring or cluster-cup stage upon the barberry, 
swollen spots are produced upon the leaves, fruit, or young 
stems. These spots upon one side bear the cups in abundance 
and upon the other side appear as pale, circular regions which 
bear the small, black pycnia. 

Upon the wheat the rust shows first its uredinia, which 
come later than the uredinia of the orange-leaf-rust, and 
are of more brownish tinge. The sori are most common 



Cereals 311 

upon the stems and leaf sheaths, more rare upon the leaf 
blade. Following this stage the black telia appear upon the 
stems and leaf sheaths, constituting the most conspicuous 
and predominating s^anptom. 

The damage by this disease is due to the inroads of the 
fungus upon the green leaf tissue, destroying the starch- 
producing power, diminishing the vigor of the plant, and 
showing its effects finally in the shrunken, shriveled grain. 

Since this rust usually appears late in the season, the 
varieties of wheat that mature early are likely to escape its 
attack to a greater extent than those varieties which are 
late in maturing. For a similar reason climatic or agronomic 
conditions which conduce to slow growth and late maturing 
of the crop favor the rust. 

Since the common barberry (Berberis vulgaris) and its 
varieties, or Mahonia is necessary to the functioning of the 
teliospores, these plants should not be tolerated.^^^ In Den- 
mark in 1903 laws enforced eradication of this barberry. 
Eleven years after we read '*^- 

''That black rust has disappeared gradually, contemporary 
with the barberry bush. 

''That the violent, destructive black rust attacks, which 
affected the whole or most of the country, mth two or three 
years interval, have now ceased. 

"That the weaker attacks which affected the grain and 
grasses and especially the oats in Jutland are now practically 
unheard of, or at least come late in the fall." 

Influenced by such evidence, in 1918 and 1919 the Federal 
authorities and those of many states, particula,rly in the 
Middle States and Northwest, took energetic measures to 
eliminate the barberry and Mahonia. Anti-barberry laws 
were passed in Saskatchewan, Manitoba, Canada, and many 
states, notably in North Dakota, Iowa, Colorado, Minnesota, 
Montana, Nebraska, South Dakota, Wisconsin, Michigan, 
lUinois. It is clear from experimental evidence that the rust 
does not commonly pass to the next crop on the seed, nor 
does it commonly overwinter in the living host plants, except 



312 Diseases of Economic Plants 

in the extreme South. The evidence is also to the effect that 
such rust as does overwinter in the South does not pass to the 
North, but that the main source of infection in the North is 
from the barberry. 

Some durum wheats are highly resistant to rust, and 
recently, by selection, the Kansas Agricultural Experiment 
Station produced a bread wheat of the Crimean group 
that under Kansas conditions was highly rust-resistant. 
Before the rust problem can be solved by breeding resistant 
plants, much fundamental knowledge must be gained re- 
garding the biologic races of the parasites and their host 
ranges. Many wild grasses propagate and spread the rust 
and, especially if they are exposed to infection from the 
barberry, may bridge the way to a wheat field. Prominent 
among those grasses are wild barley, slender-wheat-grass, 
western-wheat-grass, and wild rye grasses. Obviously they 
should be kept down as much as possible. 

Orange-leaf -rust (Puccinia triiicina Eriks.). — This rust 
of wheat and possibly of several wild grasses is the most 
common and widely distributed of all rusts of the United 
States and is especially injurious in the southern states. It is 
said by Carleton that it is not only never absent from the 
wheat fields throughout the year, but that it is sometimes 
abundant even in dry seasons. Notwithstanding its preva- 
lence its inroads upon the crop are not usually serious, and 
in no case on record has it caused shriveling of the grain such 
as is common from the black-stem-rust. 

The most conspicuous character of this rust is the presence 
of many orange-colored sori upon the leaves, especially upon 
their lower surfaces. The grayish black telia are neither 
so prominent nor so profuse as in the black-stem-rust. Both 
of these rusts possess the uredinial stage, and it is difficult 
to distinguish them apart in this condition except by the 
microscope. 

As with the rye orange-leaf-rust, this fungus also can winter 
in its live uredinial mycelium and continue to bear uredinio- 
spores throughout the year, spending its entire existence, if 



Cereals 313 

necessary, in this one stage upon the single species of host. 
While no variety of wheat is entirely proof against it, large 
difference is shown in this respect, some presenting high 
resistance, even under most adverse conditions. Early 
maturity is an important factor in evading rust. 

The following standard varieties are recommended by 
Carleton as possessing considerable resistance to the orange- 
leaf-rust in every part of the country — ''Winter wheats: 
Turkey, Mennonite, Pringles No. 5, Tieti, Odessa, Pringles 
Defiance. Spring wheats: Haynes Blue Stem, Saskatche- 
wan Fife. 

''The following varieties seem to be resistant, but have not 
yet been well established as such: Theiss, Oregon Club, 
Sonora, Diehl Mediterranean, Fulcaster, Arnolds Hybrid, 
California Spring. 

"Some of the hardy prolific sorts not yet well known in this 
country, but likely to be more or less rust-resistant after 
thorough acclimation and selection, are — Winter wheats: 
Prolifero, Banatka, Red Winter, Nashi, Tangarotto, Bearded 
Winter, Winter Ghirka, Budapest, Crimean, Yx, Belle vue, 
Talavera. Spring wheats: Alsace, Spring Ghirka. 

"Two varieties which are quite susceptible to rust, but 
which usually ripen early enough to escape the worst effects 
of it, are: Early May and Zimmerman. 

"Some others not quite so well known, but probably 
worthy of trial as rust -escaping sorts, are — Early Baart, 
Allora Spring, Kathia, Roseworthy, Japanese No. 2, Yemide, 
Canning Downs. 

"These last varieties are not likely to withstand very 
severe winters, and are therefore best adapted to southern 
districts, where they may perhaps in time become accli- 
mated. Yemide and Kathia are probably the most hardy 
of the six. Canning Downs winter-killed in one trial, even 
in Mississippi." 

Yellow-stripe-rust {Puccinia glumarmn (Schum.) E. & 
H.). — This rust, which is serious in Europe on wheat and 
barley and less so on rye and several wild grasses, was found in 



314 Diseases of Economic Plants 

Arizona in 1915 on wheat; since then, in the western United 
States, on barley, rye, and many wild grasses. On barley it 
has appeared as far east as South Dakota. 

Bunt, Stinking-smut ^~'^ {Tilletia Icevis Kiihn, Tilletia tritici 
(Bjerk.) Wint.). — Tilletia tritici causes heavy losses in the 
Northwest, T. Icevis in the eastern United States. Where 
both occur the first is known as ''low smut," the second as 
''high smut" from their respective habits. This smut (for 
practical purposes the two may be considered as one) is 
readily distinguished from loose-smut by the fact that it 
attacks only the grain, not the inclosing chaff. The head 
therefore remains of much more nearly normal appearance, 
and it is often not until the glumes have been opened, and 
their contents examined, that the presence of the smut mass is 
detected, covered with its membrane, and resembling the 
wheat grain in size and shape. It may be recognized by an 
expert observer by its peculiar, disagreeable, penetrating 
odor, and by the deeper green color of the diseased heads. 
The smut masses are often so firm as to remain unbroken 
through threshing, but they may be recognized among the 
grains by their darker color, greater plumpness, absence 
of groove and germ, and finally by crushing them and lib- 
erating the black spores. 

The disease is particularly destructive, since its presence 
signifies not only loss of grain due to replacement by smut, 
but also loss in value to the good wheat, which may be 
largely depreciated in price by the presence of the bunt. 
Often bunted wheat is worthless for milling purposes and 
even for cattle feed. Bunt constitutes, for these reasons, 
one of the worst smuts in the world. Strong fanning re- 
moves part of the smutted grains, but troublesome wash- 
ing processes must be employed to remove them all, and even 
then the results are not entirely satisfactory. The annual 
loss from bunt in the United States is about 25,000,000 bu., 
to which should be added the frequent loss from explosion 
of threshing machines, estimated at $1,000,000 in two years, 
due to the oily combustible spores. Where low smut alone is 



Cereals 315 

present and the heads only are harvested, the sickle-bar 
may be so adjusted as to leave the bunt behind. 

Many smut spores naturally find lodgment upon the sur- 
faces of healthy grains from smutted fields, or they may be 
carried from farm to farm upon the threshing machine. Upon 
planting such seed the following season these spores are 
ready to attack the seedling grain plant. The fungus, after 
gaining entrance into the seedling, grows with it throughout 
the season, and appears again at harvest time as spore masses 
within the chaff. Every grain of every head of an affected 
plant is usually smutted. 

The seedling age, like that of the oat, is the onty age sus- 
ceptible to smut infection. Treatment of seed wheat with 
formalin is usualty complete in its efficienc}^ and trifling in 
cost. In some sections of the Northwest, however, the soil 
has become so heavily infested from previous cropping and 
by '^smut showers" that formalin seed treatment is of but 
little value. In such regions early sowing and crop rotation 
are recommended. 

Loose-smut ^-^ (Ustilago tritici (Pers.) Rostr.). — Like the 
loose smut of barley, this smut seems to be increasing in 
importance. In some regions it prevails to a greater ex- 
tent than the bunt, causing at times a loss of more than a 
quarter of the crop though the loss is usually not more than 
2 per cent. Loose-smut may readily be distinguished from 
stinking-smut of wheat by the fact that the spore masses 
involve the whole spikelet, which becomes dry and powdery 
and falls away; also by its much earlier appearance in the 
field, i. e., at flowering time. The spore masses are dark, 
ohve-black, and are produced exclusively in the spikelets. 
The bearded spring wheats seem to be more susceptible 
than the blue-stem varieties, but the smut is common on all 
varieties. 

From the studies of Maddox in Tasmania, Wakagwa in 
Japan, Brefeld in Germany, and others, it was known in 1896 
that with the loose-smuts of wheat and barley, totally unlike 
the bunt of wheat and the loose-smut of oats, infection 



316 Diseases of Economic Plants 

occurs exclusively at blossoming time; that at all other 
times the plants are immune. Smut spores from near-by 
smutted heads are blown into the wheat or barley flowers. 
Infection follows. The fungus then lies dormant in the 
grain until the seed sprouts. If the grain ripening from 
such infected flowers be used for seed, the fungus develops 
in the seedling, and an infected plant, producing smut but 
no grain, results, though no external symptom of the disease 
appears until blossoming time. Conversely, if seed result- 
ing from blossoms which were not infected be used, plants 
free from smut will be raised. 

The remedy in this case, therefore, lies in the use of unin- 
fected seed. To obtain such seed, grain must be secured 
from a field in which there is no loose smut, or if this is not 
practicable, seed grain must be raised under such conditions 
as will afford clean seed. 

It has been found that while the ordinary formalin seed- 
treatment is ineffective against wheat loose-smut, the hot- 
water treatment, in modified form, is effective, though some- 
what difficult of manipulation. See p. 272. 

Rogueing or weeding out all diseased plants from the crop 
that is to be used for seed, diminishes the smut largely, but 
does not entirely eliminate it. 

A practicable, effective means, which results in complete 
and inexpensive eradication of this smut, consists of a com- 
bination of the seed plat with the hot-water treatment. 

Flag-smut ^^^' ^-^ (Urocystis tritici Koern). — Linear, black 
streaks in the leaves, much like those shown in fig. 182, 
occur on wheat. Considerable damage is reported from 
Australia, India, and Japan. Flag-smut was found in 
Illinois in 1919. The usual formalin treatment is beneficial, 
though not so complete in control as with oat smut, since 
infection occurs, to some extent, from diseased refuse in the 
soil. If badly infested, the stubble should be burned to 
destroy as many spores as possible. 

Foot-rots. ^^^' ^25,554 — These diseases are characterized by a 
brown or black-rot on the lower part of the stem, the diseases 



Cereals 317 

occurring in the fields in spots. They are known in many 
countries on wheat, oats, barley, rye, and rice, and are very 
destructive in Europe and Australia. The diseases in their va- 
rious forms have many names, among them Take-all, White- 
heads, Pietin. Any one of several fungi may cause foot-rot, 
especially when the wheat plant is weakened by adverse en- 
vironmental conditions. A foot-rot of wheat due to unknown 
cause was reported in Oregon in 1902, and one due to Hel- 
minthosporium in Illinois and Indiana in 1919. Burning of 
the stubble and crop rotation, accompanied by good drain- 
age, are recommended. 

Anthracnose {Colletotrichum cereale Manns) . — This an- 
thracnose seems to prevail on wheat as extensively as upon 




Fig. 165. — Normal wheat kernels and shriveled ker- 
nels due to anthracnose. After Manns. 

rye. The head is not destroyed, as in the case of rye, but 
general weakness of the plant and light, shriveled grain 
follows the attack. 

Powdery-mildew ^^^ {Erysiphe graminis DC). — The usual 
characters of the powdery-mildews are exhibited; a whitish, 
flour-like coating in irregular, circular spots upon the leaves 
and other plant parts. This mildew, together with the 
mildew of oats, rye, and barley, bears the same specific 
name, but upon each of these crops the form is so special- 
ized as not to transfer readily, if at all, to the other crop 
plant. Thus from the farmer's viewpoint there are prac- 



318 



Diseases of Economic Plants 



m 



tically four distinct kinds of mildew, although indistinguish- 
able to the eye. The form upon wheat grows upon all species 
of Triticum though some varieties show much more resistance 
than others. 

In damp, shaded spots the mildew is sometimes quite 
injurious, though it is rarely so over any considerable area. 

The conditions favor- 
ing the disease should 
be avoided. 

Scab ^-9 (Gihherella 
saubinetii (Mont.)Sacc., 
Fusarium). — Scab, first 
described in 1884 in 
England, seems to be 
quite generally distrib- 
uted in America, and 
is often the cause of 
large loss which, under 
conditions favorable to 
the disease, may reach 
from 10 to 30 per cent 
or higher. The loss in 
1917 was estimated as 
about 10,000,000 bush- 
els. Scab appears upon 
the heads when about 
Anthracnose on wheat stems, half ripe, as yellow or 

pink incrustations on 
the spikelets, on the bases of the glumes, or covering the 
rachis. The affected spikelets ripen prematurely and turn 
yellow or brown before the normal parts mature. After 
ripening of the head, the diseased parts appear shrunken. 
The grain itself is shrunken, covered with a thick felted 
mycelium, and is incapable of germination. 

Only a few spikelets upon the head may be affected, these 
occupying any position — basal, terminal, or intermediate 
— or the whole head may be diseased. The loss consists in 




"V 




Fig. 166. 



Cereals 319 

injury to the quality of the grain and diminution in quan- 
tity. 

Selby has shown that seedlings in the field are often killed 
by this disease, which is carried over in the seed. In this 
way as high as 5.9 per cent of death in seedlings has been 
caused. 

It has recently been shown that the fungus that causes 
wheat scab grows also on corn causing root-rot, and winters 




b a 

Fig. 167. — Wheat kernels: a, normal; h, shrunken and killed by- 
scab. After Manns. 

on corn refuse. Wheat planted in fields that bore infected 
corn becomes badly diseased. One corrective practice, there- 
fore, is to avoid sowing wheat on land so infested. 

Minor diseases 

Black-chaff ^^^' ^^^ {Pseudomonas translucens) . — As the 
wheat approaches maturity, black, sunken stripes appear 
lengthwise of the chaff. The rachis and leaves are also at- 
tacked. In severe cases the grain is shriveled. The disease 
was found in 15 states west of Indiana in 1917. Thorough 
screening and disinfection of seed by copper sulfate is ad- 
vised. Leptosphaeria leaf-blight ^''^ (Leptosphceria tritici 
(Gar.) Pass.). — The lower leaves are killed early in the 
season. Large loss is not usual. The Glume-blotch ^^^ 



320 Diseases of Economic Plants 

(Septoria sps.) is common as small, dark spots upon the chaff 
of certain varieties of wheat. Another Septoria causes leaf- 
spots, especially upon the lower leaves. Eel-worms ^"' ^^^^ ^^^ 
(Nematodes) affecting the grain in the head have been found 
in several states, in some fields causing 25 per cent damage. 
Only clean seed should be used. Crop rotation is advised. 
Ergot is occasional on wheat. The Southern-blight {Sclero- 
tium) sometimes injures the stand in the South. 



FORAGE CROPS 

This group of crops, of high aggregate value and agricul- 
tural necessity, does not possess an acreage value which 
warrants such expensive modes of treatment as spraying. 
Protection against disease here must, in general, consist in 
modifications of agronomic methods tending to produce 
thriftier, more resistant plants, crop rotation to diminish the 
parasites, variation of time of sowing or harvesting to evade 
disease. Forage diseases are especially troublesome since 
they frequently prohibit planting of certain leguminous crops 
much desired in the rotation. 

Legumes 
ALFALFA 

Leaf-spot ^^^' '^^^ (Pseudopeziza medicaginis (Lib.) Sacc.) — 
No other disease of alfalfa is so universally prevalent. It 
constitutes the most important, in most sections the only 
really important, disease of this crop. Loss in vigor of the 
plants and loss in hay, by shedding of the leaves, result. 
Pammel in Iowa in 1891 estimated the loss in some fields at 
50 per cent. It was first described in Europe in 1832, and 
noted in the United States in 1875. 

The leaves first show small brown to black spots, irregular 
or circular, which extend through the leaf and are thus 
visible from both sides. They are about 1-2 mm. in di- 
ameter, and are not sharply bordered, but shade off grad- 
ually into the surrounding tissue. With a hand lens very 
small, spore-bearing organs may be seen in the centers of 
the older spots, first as shiny amber-colored elevations. 
These elevations soon crack open and expose very small, 
cup-shaped sporiferous bodies, which remain surrounded by 
portions of the ruptured epidermis. Badly diseased leaves 

321 



322 Diseases of Economic Plants 

usually turn yellow and fall off. Spots upon the stems show 
the same general character as those upon the leaves. 

The lower leaves, and the leaves of older plants, are most 
subject to the leaf-spot. Plants late in the season, as of 
the second and third cuttings, suffer much more than earlier 
in the season. These crops, especially in a dry season, if 
allowed to stand a little too long before cutting may be badly 
spotted, and the loss in hay, through fallen leaves, may be 




12 3 4 

Fig. 168. — Four alfalfa leaf-spots due to: 1, Ascochyta; 2, Pseudope- 
ziza; 3, Cercospora; 4, Stagonospora. After Stewart and others. 

considerable. The plants are never killed by this disease, 
though young fields which have not yet become well estab- 
lished may be ruined. 

Its mode of dissemination is unknown, and seed treatment 
is useless as a preventive. 

The only practicable treatment is to mow down badly 
diseased plants with the hope that the new shoots which 
spring forth may overcome the disease. If the disease 
appears just before cutting time, the mowing should be 
hastened a few days in order to avoid loss from leaf shedding. 

Yellow leaf-blotch ^'^^ {Pyrenopeziza medicaginis Fcl., 
Sporonema) . — This disease is known from Vermont to the 
Pacific, in Europe and South America, and under certain 



Forage Crops 323 

conditions does more damage than leaf-spot. The spot 
produced is deep yellow, verging to orange, and bears nu- 
merous orange-colored pycnidia. The fungus winters on 
infected leaves. Early cutting is beneficial. 

Wilt ^^'^ (Sclerotinia trifoliorum Eriks.). — This wilt, which 
in some respects resembles lettuce drop, has been noted on 
alfalfa and the clovers, red, white, crimson, bastard, mam- 
moth, and alsike, in several widely separated sections of the 
United States and Europe. 

It kills the plants, and under favorable weather conditions, 
the chief factor of which is a humid atmosphere, it may ex- 
tend from plant to plant and involve large areas in the field. 

Plants may show a variety of sjanptoms. Sometimes the 
leaves droop, and become matted together in a sodden mass 
at the base of the plant, and overgrown with a white cotton- 
like layer of mycelium, in which black sclerotia, similar to 
those described under lettuce, are found. At other times the 
stems may be the point of attack, showing dead, brown sec- 
tions covered with the mycelium and bearing sclerotia. 
Upon splitting a stem open the central part may be found 
filled with mycelium and with occasional sclerotia about the 
size of a grain of wheat. The white mycelium and black 
sclerotia are absolutel}' diagnostic. 

Under unfavorable weather conditions the disease may 
die out and fail to reappear, but if the weather is favorable 
to this fungus, the wilt may reappear year after year with 
increased severity, involving larger and larger areas. 

Stewart, French, and Wilson reported large areas where 
50 per cent of the stalks were killed, though later the field 
recovered entirely. 

Where the disease is troublesome, rotation of crops and 
deep plowing to bury the sclerotia seem to be the only re- 
course. Isolated, infested areas may be cleaned out by burn- 
ing. 

Texas root-rot ^^'^^ {Ozonium). — This rot is a soil disease, 
which in its general characters is identical with that so 
disastrous upon cotton and the treatment applied to cotton 



324 



Diseases of Economic Plants 



is the only one to be recommended for alfalfa. It has been 
very destructive in Texas since 1892. 

Anthracnose ^^^ (Colletotrichum trifolii Bain) . — Alfalfa 
anthracnose was first mentioned in 1905 by Bain and Essary, 

who stated that it was prev- 
alent in Tennessee in 1906 
and was one of the chief 
causes of alfalfa failures in 
that state. It has also been 
noted in destructive form 
in Virginia and New York. 
It appears as elliptical, 
sunken spots, 5-6 mm. 
long, upon the stems. The 
spots are gray and have 
dark acervuli scattered 
over them. Where the 
disease becomes aggressive, 
dead or withered stalks or 
plants are seen scattered 
over the field. These stalks 
arise from diseased crowns, 
which are characterized by 
blackening of the woody 
parts, below the point 
where the stalks are at- 
tacked. The only remedy 
seems to be the use of re- 
sistant varieties. 

Blight ^^^' ^^^ (Pseudomo- 
nas medicaginis Sack.). — 
From Colorado Paddock, 
in 1906, described a severe 
disease of alfalfa which has 
been noted for several successive years. It is due to bac- 
teria and in its early stages produces a watery, semi- 
transparent, yellowish to olive-green appearance along one 




Fig. 169. — Alfalfa crown-wart. 
After U. S. Department of Agri- 
culture. 



Forage Crops 325 

side of the stem of the plant. The plants are at first 
weak, the stems light colored, later discolored or black- 
ened. Drops of thick fluid exude from the stems and dry 
upon them, giving a glistening appearance as if they were 
varnished. The chief damage is to the first cutting, though 
in subsequent years the plants may die from decay of the 
crown, or roots, or from loss of nutrition. Infection takes 
place chiefly through rifts in the epidermis due to frost, 
thereby affording access to wind-borne bacteria. 

Crown-wart ^^^ {Urophlyctis alfalfce (Lag.) Magn.). — 
The chief diagnostic character is the presence of numerous 
galls at or near the base of the stem. They vary greatly in 
size from that of a pea to an orange. Diseased plants have 
brown, dead stems, or stems that are weak and bear yellow 
leaves. The disease apparently originated in South America, 
is now widely distributed in Europe and was first noted in the 
United States, in California, in 1909, later in Arizona, Oregon, 
and Utah. 

Dodder "^^ {Cuscuta sps.). — Dodder, or love vine, is a 
parasitic, flowering plant. Its yellow, threadlike stems coil 
closely around the alfalfa stems, and take nourishment from 
them. It reproduces by seed, and the seed may readily pass 
with alfalfa seed unless very carefully inspected. The 
parasite is absolutely ruinous to the portions of the field 
that it infests and, since it spreads rapidly, it is a serious 
enemy. 

If dodder occurs in spots, these should be dug over or 
burned over before it ripens its seed, using kerosene and 
straw to insure heat sufficient to kill every plant, with a 
margin of a few feet entirely around the infested spot. 
Badly infested fields should be plowed up. 

Minor diseases 

Root-rot, wilt (Fusarium sp.). — The first symptom of 
this wilt is a yellowing of the outer leaves which gradually 
spreads until all of the leaves and stems become discolored, 
wilt, and die. This rot is said to be quite generally destrue- 




1 2 3 

Fig. 170. — 1, Alfalfa seed; 2, seed of large- 
seeded dodder; 3, seed of small-seeded dodder, 
natural size. After Stewart and others. 




Fig. 171. — Alfalfa plant and dodder. After Stewart 
and others. 



Forage Crops 327 

tive in Arizona. It is a soil disease, and its general characters 
are those indicated on p. 26. 

Root-rot (Rhizoctonia crocorum DC). — Similar to the 
effects of Rhizoctonia upon so many other hosts, the disease 
consists primarily of a root-rot in which the diseased parts 
are coated with matted strands of the fungous mycelium, 
usually brownish red or violet in color, accompanied by 
sclerotia. The tops of plants so diseased turn yellow and die. 

The very aggressive fungus migrates through or over the 
soil to adjoining plants, and the affected spot in, the field 
thus enlarges, 'sometimes at a rate of 7 m. radially per year. 
Though long known in Europe, it has not yet appeared in 
many parts of America. 

Rhizoctonia root-rot is a typical soil disease and is kept 
alive in the soil by its sclerotia, which maylive at least two or 
three years. The general suggestions given under soil dis- 
eases apply. 

Ascochyta leaf-spot {Ascochyta medicaginis Bres.). — This 
leaf-spot has been noted in North Carolina, and what is 
probably the same disease, also in New York. The spots are 
irregularly circular except where they occur on the edge of 
the leaf, light brown in color, and bear small black dots. 

Cercospora leaf-spot (Cercospora medicaginis E. & E.), 
which appeared in Delaware in 1889, has also been noted in 
New York and New Jersey. The leaf-spots are nearly circu- 
lar, smoky brown to black, from 0.5-1 mm. in diameter, and 
show equally well from either surface of the leaf. They have 
no well-defined borders, but shade into the surrounding 
healthy tissue. Affected leaves turn yellow and die. It ap- 
pears to be disseminated on the seed. Seed disinfection is 
therefore recommended. A leaf-spot has also been described 
due to Pleosphcerulina hriosiana Poll., and others due to 
Septoria and Macrosporium. 

Downy-mildew {Peronospora trifoUorum De Bary) is a 
serious pest on clover in Europe and has been reported in 
America from Colorado, Kansas, New York, and North 
Carolina, though it has not yet been destructive in this 



328 Diseases of Economic Plants 

country. The affected parts of the leaf turn yellowish gray to 
purple, and are frequently curled. The leaves, as seen from 
below, are coated with a downy fuzz, violet colored when old. 

Rust {Uromyces striatus Schr.) may be recognized by the 
typical rust sori, which are present, in this case, chiefly upon 
the lower sides of the leaves. The cluster-cup stage is found 
on Euphorbia. Anthracnose {Gloeosporium medicaginis E. & 
K.). — Black, rather prominent acervuli appear chiefly upon 
the lower surfaces of leaf-spots. The lower leaves often 
turn yellow and die. Seed-mold (Alternaria sp.). — Brown, 
dead, shriveled seeds are often noted in samples of alfalfa 
seed. Such seeds, if planted, develop, apparently from 
within, a dense black mold. 

Damping-off (Rhizoctonia sp. and Pythium debaryanum 
Hesse) is caused chiefly by the two fungi named. It has 
been known to affect alfalfa seedlings in the greenhouse, 
and it may occur to some extent in the field, especially the 
form caused by Rhizoctonia. 

Stagonospora leaf-spot (Stagonospora carpathica Baeu.) 
has been noted only in New York. Stewart, French and 
Wilson characterize this leaf-spot as follows: Unlike the 
Ascochyta leaf-spot, this disease attacks chiefly green leaves 
in the upper part of the plant. The spots are circular, 
1-3 mm. in diameter, and usually light brown with a narrow 
border of dark brown. Each spot bears several light brown 
pycnidia visible on both surfaces of the leaf. Yellow-top 
may appear simultaneously over whole fields. The cause is 
unknown. White-spot is common but also is of unknown 
cause. 

CLOVER 

Black-mold {Phyllachora trifolii (Pers.) Fcl., Polythrin- 
cium). — Common red clover, crimson clover, white clover, 
alsike clover, and several other related plants are affected by 
this mold. The chief symptoms are pale spots upon the upper 
sides of the leaves accompanied by black dots on the lower 
sides. These spots at first glance so strongly resemble the 



Forage Crops 



329 



sori of the rusts as to lead the casual observer to mistake the 
disease for a rust. Though the disease is often of considerable 
damage, no treatment is known. 

Wilt ^^^ (Sclerotinia trifoliorum Eriks.). — The fungus caus- 
ing this wilt is probably identical with that of the wilt of 
alfalfa. It was first noted in America, in Delaware, by 
Chester in 1889, later in New Jersey by Halsted. 

The affected plants wilt and rot to the ground. White 
mats of myceUal threads, and later black sclerotia, are 
found upon or within 
the dead stems. Scle- 
rotia are especially 
abundant at the bases 
of diseased stems. 
Disk-like bodies, simi- 
lar to those described 
in connection with 
lettuce drop, develop 
from the sclerotium 
and bear spores which 
spread the infection. 
While this malady has 

been very destructive in Europe upon several varieties of 
clover, it is not yet of wide distribution in America, though 
it has appeared as a serious pest in a few fields. 

It is exceedingly difficult to eradicate when it has once 
gained foothold, and the European recommendation is to 
avoid planting the infested fields to susceptible crops. 

Rust (Uromyces sps.). — The clover rusts are most in- 
jurious to the second cutting, to which they may cause a 
damage of 20 or even 50 per cent if conditions favorable to the 
disease — damp, cool weather — obtain. These rusts, long 
known in Europe, were first reported in America in 1884. At 
the present time they are found upon red, white, crimson, and 
alsike clovers over a large part of the United States, though 
of different species, or at least different biologic races upon 
some of the different hosts. 




Fig. 172. — - Clover leaf showing spots of 
black-mold. Original. 



330 



Diseases of Economic Plants 



These are true rusts, and on the white clover possess all 
of the three stages, cluster-cup, summer or uredinial, and 
winter or teliospores. They attack all green parts of the 
plant. The most conspicuous and destructive stage is the 
uredinial, which is marked by profuse, circular or elongated, 
chestnut-brown, powdery sori. These may be few and 
scattered, but more often they are abundant, nearly covering 
the leaf, which turns black, dies, and shrivels. The rust is 
conveyed from plant to plant throughout the summer by 
spores of this stage. 

The teliospores or urediniospores may appear in the same 
or separate sori and in either event the teliospores appear 

later in the season. They are rec- 
ognized by their darker brown 
color. The cluster-cup stage, which 
is less abundant and less injurious 
than the other stages, may often 
pass unnoticed. It appears first as 
pale, swollen regions upon the leaf 
or petiole. These regions soon 
show the characteristic cups with 
orange-colored spores. The cluster- 
cup stage, though not known on 
red clover, predominates in the 
early spring upon many other 
varieties; but the uredinial stage 
soon gains the ascendancy over it. 
All three forms may be produced 
side by side, to some extent, 
throughout the summer. Hiber- 
nation probably occurs in two 
ways, by the teliospores and by the 
mycelium, which may remain alive 
in the affected parts over winter. 
Anthracnose ^^^ {Colletotrichum trifolii Bain). — This an- 
thracnose is now known on clovers and alfalfa in Tennessee, 
Ohio, West Virginia, Arkansas, Kentucky, and Delaware. 




Fig. 173. — Anthracnose 
on red clover stem and 
petiole. After Jackson. 



Forage Crops 331 

It is first found chiefly upon the leaf stalks, later upon the 
stems, near the surface of the ground and just below the 
flower clusters, as elongated sunken spots, which result 
eventually in the death of the whole plant. It frequently 
causes great loss, and is said, by Bain, to be the most serious 
plant disease in Tennessee. Alsike clover is nearly immune. 
Hope lies in the use of resistant varieties. 

Anthracnose (Gloeosporium caulivorum Kirch.). — Long, 
brown to black, sunken spots upon stems and petioles, caus- 
ing death of the more distal parts, are diagnostic characters 
of this anthracnose, which was first reported in the United 
States by Sheldon in 1906, and has since been noted as 
serious in a number of states. 

Minor diseases 

Leaf-spot ^^^ (Pseudopeziza irifoUi (Biv-Bernh.) FcL). — • 
This leaf-spot much like that of alfalfa occasionally causes 
considerable damage. A Cercospora leaf- spot is also re- 
corded. Black-mold (Macros par iiim sarcinceforme Cav.) is 
widely distributed as the cause of concentric spots on leaf 
and petiole. Scab (Gibherella sauhinetii, Fiisarium) . — This 
parasite of cereals is also known to cause depressed, oblong 
spots upon clover. See wheat. Broom-rape {Orobanche 
minor L.) is similar to that upon tobacco. See p. 259. Root- 
rot (Rhizodonia) is sometimes injurious. Dodder. See 
alfalfa. 

COWPEA 

Wilt ^^^ (Fusarium vasinfedum Atk.). — This disease, 
closely like wilt of cotton, okra, and watermelon, is not com- 
municable from one of these plants to the other, though it is 
identical with the wilt of the soy bean. 

It first appears when the plants are about six weeks old. 
Up to this time they grow well and appear healthy. Scat- 
tered plants then begin to drop their leaves, the lower ones 
falling first. Growth is checked, and the stem shows a faint 



332 



Diseases of Economic Plants 



reddish brown tinge. After the leaves have fallen the stem 
dies and becomes covered with a light pink coating of the 
spores of the wilt fungus. The spread of the disease is more 
gradual and less conspicuous in the early part of the season, 
but after the peas begin to set fruit they succumb rapidly, and 

a field that in July gave 
promise of a fine crop may be 
entirely dead before Septem- 
ber without having matured 
a pod. The disease usually 
appears in spots, like the 
cotton wilt, and these dis- 
eased areas may spread until 
a whole field is involved. 

In moderate cases, or 
where the varieties planted 
are less subject to disease, 
only the weaker plants are 
killed, while the rest are 
dwarfed and their yield re- 
duced. Careful examination 
of the roots shows that many 
of the small, lateral roots are 
dead, small tufts of roots 
marking the points of infec- 
tion (Fig. 174) . This tufting 
of the rootlets is similar to 
that produced on cotton by 
the cotton-wilt fungus. 
In all cases the veins of the stem are brown, and the dis- 
ease may clearly be distinguished by cutting across the stem 
to observe whether the color of the wood is normal. This 
discoloration, which may often be seen through the translu- 
cent stem of the cowpea, is characteristic of this class of 
diseases. The name '^wilt" is somewhat misleading, since 
the leaves usually drop off before there is any conspicuous 
wilting. 




Fig. 174. — Roots of diseased cow- 
pea at left; healthy roots on the 
right. After Orton. 



Forage Crops 



333 




334 



Diseases of Economic Plants 



The causal fungus is spread by the ways suggested 
under soil diseases. The disease is now known in most 
of the Southern States from North Carolina to Florida, 
and west to Texas, and is yearly noted in new lo- 
calities. 




Fig. 176. — Nematode galls on roots of Unknown cowpea. After 

Lewis. 

Owing to the all-important position the cowpea occupies 
in southern agriculture as a nitrogen crop, where the best 
rotation demands its frequent recurrence upon the same 
soil, the disease is of peculiar moment. 

No remedy is known except the use of the Iron cowpea or 



Forage Crops 



335 



its derivatives, the resistance of which was noted by WilHams 
of South Carohna in 1900. 

Root-knot (nematodes) is especially destructive on cow- 
peas. The Iron or Brabham varieties are resistant. 




Fig. 177. — Roots of the Iron cowpea free from nema- 
tode galls. After Lewis. 

Minor diseases 

Leaf-spot {Amerosporium oeconomicum E. & T.). — This 
disease is readily distinguished from the angular leaf-spot in 
that the spots are circular, are of shiny whiteness, and are 
studded all over with black pycnidia, smaller than a pinhole 
(Fig. 178). The disease is often abundant, but is usually not 
so serious as the angular leaf-spot. 







Fig. 179. — Cowpea leaflet spotted Fig. 180. — Leaflet of cowpea showing 
with powdery-mildew. Original. Carcospora spots. Original. 



Forage Crops 337 

Powdery-mildew {Erysiphe pnlygoni DC). — The white 
spots of this mildew are strictly circular when j^oung, but 
as they enlarge they coalesce and cover the whole upper 
surface of the leaves with a white powder. 

The disease is very widespread, but even in the worst 
seasons does not do much injury. 

Angular leaf-spot (Cercospora cruenta Sacc). — The an- 
gular leaf-spots of this disease are a familiar sight in most 
cowpea fields. They are of various colors above, chiefly 
reddish, and are gray to purplish or slate-colored below. 
The damage is rarely very great. In some instances the at- 
tack may proceed to the stems, where, especially at the base, 
it may cause cracking and result in such lowering of the vigor 
of the plant as to cause shedding of leaves and failure to 
properly fill the pods. The loss of leaves is of course serious 
to the hay value of the crop. 

Root-rot (Thielavia) ; a Phyllosticta leaf-spot and a Sep- 
toria leaf-spot also occur. Streak. See sweet pea. 

JAPAN CLOVER (Lespedeza) 

Powdery-mildew {Microsphcera diffusa C. & Pk.). — 
The usual characters of the powdery-mildews distinguish 
this disease sufficiently. The injury to this valuable southern 
forage plant, while considerable, is never sufficient to call 
for treatment. 

SOY BEAN {Soja) 

Bacterial blight ^^2-534 (j>seudomonas glycineum Coerper) . — 
Small, angular spots, 1-2 mm. in diameter, at first water 
soaked, translucent, later yellow or brown and eventually 
brown or purplish black, occur on the leaves and pods 
accompanied by a bacterial exudate. 

The disease has been reported from Nebraska, Connecti- 
cut, Wisconsin, and North Carolina. 

It is thought to be seed-borne. 

Wilt. See cowpea. 



338 Diseases of Economic Plants 

VETCH 

Spot (Protocoronospora nigricans A. & E.). — Upon the 
stems, leaves, and bracts of vetch very characteristic, long, 
narrow, or elliptical spots are formed, frequently with a dull 
purple border, and usually with a white center. When on 
the pods, they are obliquely situated. When old, they ap- 
pear as black, oblique lines. No serious damage has been 
reported. 

Downy-mildew {Peronospora vicice (Berk.) De Bary); 
Powdery-mildew (Erysiphe); Rust (Uromyces sps.), and 
Leaf-spot {Mycosphwrella) see pea, are of minor importance. 

Grasses 

Many of the diseases listed below on special grasses should 
perhaps be considered as general grass diseases. Thus the 
smut, Ustilago striceformis, is known on many genera of 
grasses. Grasses in general are susceptible to powdery- 
mildew, Phyllachora, Ergot, and rust. The biologic rela- 
tionships of but few of these have as yet been studied on 
account of their comparatively small economic significance. 

BARNYARD-GRASS {Panicum) 

Smut {Ustilago crusgalli T. & E.) is common and is readily 
recognized by the usual smut characters. No treatment is 
recommended. 

BLUEGRASS (Poa) 

Rust (Puccinia poarum Niels.). — The uredinia of this 
rust take even greater prominence than do the uredinia of 
other rusts; indeed other forms of spores are almost entirely 
absent in most parts of the country, throwing the burden of 
perpetuation of the species entirely upon the uredinial 
mycelium and its spores. This stage is known to be peren- 
nial as far north as Washington, D. C., Nebraska, and Min- 
nesota. The secia occur on Tussilago. 



Forage Crops 339 

The rust is destructive, but seems to be limited to this one 
host. 

Smut. See timothy. 

Anthracnose. See rye. 

Minor diseases are caused by Uromyces poce Rab., Phyl- 
lachora poce (Fcl.) Sacc, and Ergot. 

CRABGRASS 

Blast (Piricularia oryzce Cav.). — This is probably iden- 
tical with rice blast. See p. 300. 

JOHNSON GRASS. See sorghum, p, 307, which has similar 
diseases. 

MILLET. See p. 295. 

ORCHARD -GRASS (Dadylis) 

Leaf-spot {Scolecotrichum graminis Fcl.). — Elliptical, 
dead spots may appear upon orchard-grass and on several 
other grasses, conspicuous upon the lower outer leaves. 
Death of the leaf follows sometimes, starting at the leaf tips 
and reaching to the base. In conditions favorable to the 
disease whole plants are involved. The spots, before they 
become confluent, are of quite characteristic appearance: 
large, dark brown to purplish brown. When old, they usually 
show at their centers spots of gray or white, and these spots 
may be marked with small, black specks arranged in rows 
lengthwise of the leaf. 

Black-stem-rust {Puccinia graminis Pers.). — This rust 
fungus may be either of the oat, orchard-grass, or Agrostis 
strain. 

Crown-Rust {Puccinia coronata Cda.). — See oats, p. 298. 

Anthracnose. See rye, p. 307. 

Rathay's disease {Bacterium rathayi (EFS.) ) ^"^^ develops 
with thick layers of bacteria on the surface of the plant, 
causing an unusual type of plant disease. 



340 



Diseases of Economic Plants 



PASPALUM 

Ergot ^^^ {Claviceps paspali S. & H. and C. rolfsii S. & H.). 
— The ergots displacing the grain are somewhat smaller than 
a pea, irregularly globular in outline, and pale yellow in 

color. Stock poisoning 

from pasturing on grass 
bearing these ergots is com- 
mon in the South. Mow- 
ing the green heads before 
the ergot develops will les- 
sen the danger. 

QUACKGRASS (Agropyron) 

Smut ( Urocystis agropyri 
(Preuss.) Schroet and Usti- 
lago) . — These smuts re- 
semble each other in the 
general appearance of the 
sori, though microscopi- 
cally the characters are 
quite different. 




Fig. 181. — ^ Ergot on Paspalum. 
After Beal. 



REDTOP (Agrostis) 

Black-stem-rust {Puccinia graminis agrostis Erks.). — 
The rust is identical with that upon wheat and oats, though 
infection does not readily pass from one host to the other. 

Smut {Ustilago striceformis (West.) Niessl). — This is 
the smut described under timothy. It has been known 
to affect 30 per cent of the plants, and to reduce the seed 
yield from 300 hundredweight to 70 hundredweight. 

Anthracnose. See rye. 



TALL OATGRASS 

Smut (Ustilago perennans Rostr.). — This smut closely 
resembles that of oats, though the flower parts are not so 
completely destroyed as in oat smut. The disease is peren- 



Forage Crops 



341 



nial in its perennial host, and smutted plants bear smut, 
year after year. 



TIMOTHY (Phleum) 

Smut ^^^ {Ustilago striceformis (West.) Niessl). — This smut 
occurs chiefly upon the leaves, more rarely upon other parts 
of timothy, as well as 
upon many species of 
Agrostis, Poa, Elymus, 
Bromus, Dactylis, Fes- 
tuca, in Europe, Australia, 
and generally throughout 
the United States. The 
spore masses form long 
black lines upon the leaf, 
and by merging and rup- 
turing reduce the leaf to 
a torn, blackened state. 
The affected plants are 
small, weak, and often fail 
to make seed and the hay 
value is thus lowered. 
The disease is perennial 
within the host. Infec- 
tion takes place in the 
blossom, resulting in a 
seed bearing the myce- 
lium of the smut. Hot- 
water treatment of seed 
(cold water 6 hours, 52° 
C. (123° F.) 15 minutes) 
gives promise of success. 

Rust "^^^ {Puccinia gravi- 

ini s phleipratensis) . — ^ , ^^ r. . n ^. ., 

rp,. X • 1 Fig. 182. — Son of Ustilago striaefor- 

This rust m^ general re- ^^^ -^ i^^^,^ ^^ ^^^^^^ ^^^^^ 

sembles the black-rust of Osner. 




342 Diseases of Economic Plants 

the grains. It was first reported in 1882 and has of recent 
years increased rapidly. It can be transferred easily to 
various grasses. The secial host is not definitely known, 
but probably is not the barberry. The rust winters mainly 
in the uredinial stage. 

A Stripe-blight (bacteria) is recorded. 

Powdery-mildew is common but not serious. 

Anthracnose. See rye. 



FIBER PLANTS 
COTTON ^^^ 

Wilt ^^^ (Fusarium vasinfedum Atk.). — The cotton wilt, 
now widely distributed and yearly preempting more territory, 
is caused by a fungus that plugs the water ducts in the veins 
of the stem and cuts off the water supply to the parts above, 
always reducing the vigor of the plants and usually resulting 
in speedy death. 

Soil which produces a diseased crop one year is so infested 
with the causal fungus as to insure its reappearance in more 
extensive areas in subsequent croppings. The destructive- 
ness of a disease, which takes not only the crop, but in part 
the usefulness of the soil as well, cannot be estimated. Its 
injury can only be realized by those who have experienced its 
effects. 

Wilt has long been known by Southern cotton planters, 
both on cotton and okra, and is now prevalent in many sec- 
tions of Alabama, Arkansas, North Carolina, South Carolina, 
Georgia, Louisiana, and probably throughout the whole 
cotton belt. Many foreign countries also record it. Loss in 
Georgia was estimated as $1,000,000 annually, prior to the 
use of resistant varieties. 

The first indication of wilt appears as a yellowing of the 
lower leaves at the edges or between the main ribs, which 
portions may become almost white; later they turn brown 
and die. A single leaf often presents the three conditions, 
green (healthy), yellow (sick), and brown (dead), in bands 
side by side, parallel to the main ribs and radiating from 
the leaf stem. The dead parts may break away, leaving the 
leaf ragged. The upper leaves rapidly follow the course of the 
lower leaves. Badly affected leaves fall away, leaving only a 
bare stalk. In mild cases, where the disease runs its course 

343 



344 



Diseases of Economic Plants 



more slowly, the intervals between the different stages are 
more prolonged. 

In light sand the disease may progress very rapidly and 
may consist of two stages only, the sudden wilted condition 
followed by speedy death. The final diagnostic symptom of 
the disease, however, as in the case of many other wilts, is 
the darkening of the affected veins, which change from the 
normal white to light brown or black. Though in most 
cases the plant dies, occasionally one revives and seems to 




Fig. 183. — A variety of cotton resistant to the wilt; note the 
complete failure of the other varieties. After Orton. 

outgrow the disease. In such plants relapses may follow, 
showing somewhat different symptoms, among them decay 
of the boll, and a different sequence of color changes. 

Rotation of crops should be practiced, the diseased plants 
should be pulled and burned to check the spread of the 
disease in the soil, and in general the recommendations 
given under soil diseases should be followed. Cotton follow- 
ing cowpeas infected with root-knot, is highly susceptible. 
Therefore, only cowpeas resistant to nematodes should be 
used in cotton rotation (Fig. 177). The ultimate solution of 
the question must be in the employment of resistant varieties. 



Fiber Plants 345 

Several such have been bred by the United States Depart- 
ment of Agriculture. 

Anthracnose ^"^' ^"^ {Glomerella gossypii (South.) Edg., 
Colletotrichmn) . — The causal fungus of this disease was first 
described in 1890. It is very destructive in some localities 
and prevails throughout a large portion of the cotton belt 
of the United States and in the West Indies. The estimated 
loss for 1917 was 2.84 per cent or 364,000 bales. 

It is most conspicuous upon the bolls, where it produces 
unsightly ulcers, at first black, and later covered with a pink 
coating. The ulcers have dark brown to black, watery bor- 
ders and vary in diameter from a few millimeters to an area 
involving the entire boll. When small, the spots are reddish 
and slightly depressed. Attacks upon young bolls stop their 
growth and induce premature ripening and imperfect open- 
ing, or the bolls may die and decay without opening at all. 
In such bolls the fungus is found upon the lint and seed 
within. Upon the stems the fungus is limited mainly to 
injured parts, leaf scars, etc., and to very young, tender 
plants, causing damping-off. Here it is accompanied by 
reddening and by shrinkage in longitudinal lines. This 
disease upon young plants usually follows the use of dis- 
eased seed. Upon old stems it causes blighting of the bark, 
which becomes reddish brown and dies. 

The attack upon the leaves as upon the stems is mainl}^ 
limited to injured or weak parts. The seed leaves, being 
in a state of weakness, are especially susceptible to the 
fungus, which develops here with characters very similar 
to those on the stem and the boll. The leaves sometimes 
have a scalded look, assume a yellowish or leaden green 
color, wither and die, much as though frosted. 

There is evidence that the disease is largely carried from 
year to year in the seed and may be spread to clean seed, 
also, in the gin. Therefore, only seed from healthy fields and 
seed that has been ginned only where healthy cotton has been 
ginned should be used. 

Since the spores on the seed are short-lived, cotton seed 



346 Diseases of Economic Plants 

three or four years old, still of satisfactory viability, is free 
from infection. Crops should be rotated and seed bred on 
isolated clean plats. Treatment with commercial sulfuric 
acid to remove the lint and kill the spores has given some 
success. Hot-water seed treatments are also beneficial 
against this and other cotton, seed-borne diseases. The 
temperature should be kept as nearly 65° C. (149° F.) as 
possible for fifteen minutes. Different varieties of cotton 
show different resistances to heat and their germination 
should be tested after treatment. 

Boll-rot "^ {Diplodia gossypina Cke.). — This is chiefly a 
black-rot of the bolls, which are thickly studded with pyc- 
nidia. These exude such quantities of black spores as to 
appear smutty. The entire contents of the boll also turns 
black. Similar effects are less common on the stem. The 
disease is cause of considerable loss in Louisiana. Fusarium 
boll-rot {Fusarium sps.). — This usually follows injury of 
some kind and the fungus is really a saprophyte. Other boll- 
rots are produced by Rhinotrichum, Volutella, Sclerotium, 
Olpitrichum, Botryosphaeria, and even by the gill fungus 
Schizophyllum. 

Texas root-rot ^^' ^^' ^'^^' ^^^ {Ozonium omnivorum Sh.). — 
The first technical description of this disease was given by 
Pammel in 1888. It has since been the subject of many 
papers, and is known to occur in very destructive form in 
Texas, Oklahoma, New Mexico, and Arizona, though it has 
not been seen east of Texas. The estimated loss from this 
root-rot in 1906 in Texas was about $3,000,000. Some 
planters regard it as a worse enemy than the boll weevil. 

In this disease a few of the plants may wilt and dry up 
in a day. Later, many plants suffer a similar fate, resulting in 
irregular spots of disease in the field, marked by the presence 
of numerous standing, dead plants. The plants succumb with 
marked rapidity on hot days following rain, not so rapidly in 
continuous dry weather. Especially after a rain, living 
plants surrounded by dead ones may show symptoms of the 
disease in the form of dense sterile mycelium upon the tap 



Fiber Plants 347 

root. All diseased plants have diseased roots marked by 
injured rootlets and shrunken tap roots, accompanied by 
depressed spots which are at first bordered by red dis- 
coloration. The causal fungus is also apparent here, at 
first as a white mold which later turns brown or yellow 
and is finally accompanied by wart-like sclerotia. En- 
largements, from which new roots are put forth, often occur 
near the soil surface. Even the lint of the diseased plants is 
affected, the fibers being wider and larger, and the spirals 
fewer and more uneven, than upon healthy plants. The 
disease is truly of the soil, and the affected soil centers en- 
large yearly as in other soil diseases. It is subject to the 
modes of dissemination suggested on page 29. 

Extreme precaution should be exercised against the use, 
for the purpose of legume inoculation, of soil which may 
possibly be infested with the disease. This warning is 
particularly necessary in view of the fact that alfalfa is 
affected by the same disease, and the causal fungus is now 
present in many alfalfa fields. 

As to treatment, rotation with immune crops (see p. 23) 
in conjunction with deep fall plowing is recommended. 
To quote from Shear and Miles: '^ Rotation with immune 
crops at Terrell, Tex., resulted as follows: 1904, planted to 
cotton, about 95 per cent of which was killed by root rot; 
1905, planted to corn; 1906, planted to wheat, followed by 
sorghum the same season; 1907, cotton again planted, 
with the result that, as nearly as could be estimated, less 
than 5 per cent of the cotton was dead at the close of the 
season. 

'^Land badly infected with the root rot was plowed seven 
to nine inches deep November 11, 1906, at Petty, Tex. In 
experiment No. 1 the deep-plowed plat showed 42.75 per 
cent less dead plants than the adjoining check plat which 
received the customary tillage. In experiment No. 2 the 
deep-plowed plat showed 43 per cent less dead plants than 
the adjoining check plat, and in both cases a much larger 
amount of cotton was produced on the dead plants on the 



348 Diseases of Economic Plants 

treated plats, because these plants did not die until later 
than those on the untreated plats, and therefore had greater 
opportunity to mature their bolls." 

Root-knot (nematodes). — See p. 24. This knot is par- 
ticularly destructive on cotton, not only because of the 
direct injury it does, but also because root-knot greatly in- 
creases the susceptibility of the cotton to wilt. All means to 
hold the development of the nematodes in check should be 
employed (pp. 24-25), particularly the use of nematode- 
resistant varieties of cowpeas in the cotton rotation. 

Minor diseases 

Frosty-mildew {Septocylindrium areola (Atk.) P. & G.). — 
This leaf-spot is limited sharply by the smaller veins, and 
bears upon the lower surface numerous colorless spores upon 
colorless hyphse, thus lending a frosted appearance. Seen 
from above, the spots are light yellow or of a paler green than 
the normal leaf tissue. Widespread, though not especially 
destructive, it does not usually attract the attention of the 
planter. 

Leaf-blight {Mycosphcerella gossypina (Atk.) Earle, Cer- 
cospora) . — The fungus which causes this disease was first 
described from Carolina specimens in 1883, at which time its 
presence was recognized in South Carolina, Georgia, and 
Florida. The disease prevails in all cotton sections of the 
United States, appearing first in damp localities upon the 
lower leaves, and with the progress of the season, spotting 
all of the leaves more or less. The leaf-spots appear at first 
as small red dots, which finally, as they enlarge, bear brown 
or white centers with a characteristic red border. A copious 
development of dark hyphse upon the centers later gives 
them a blackish hue, and numerous white spores give 
these hyphse a white coating. The old diseased centers 
of the spots are brittle and frequently break away, leaving 
perforations. The disease is widespread but unimportant, 
since it is largely limited to weakened tissues, especially 
to spots produced by cotton mosaic. 



Fiber Plants 349 

Angular leaf-spot ^^^' ^^^ (Pseudomonas malvacearum EFS). 
— This disease was first described in 1891, and is widely 
distributed in the cotton producing states, in Natal and 
the West Indies. The diseased areas appear as angular 
leaf-spots bounded by the veins and are of a watery ap- 
pearance. They may be scattered over the leaf, or they 
may be nearly contiguous and later become confluent, 
resulting in irregular dead patches. Frequently they are 
most numerous adjacent to the main ribs, and result in 
long, irregular, dead, black regions. The dead tissue is 
brittle and often falls away, causing holes or ragged edges. 
Badly affected leaves fall early and loss of 50 or 60 per cent 
of the leaves is not unusual. When on the boll, the spots 
may be a centimeter in diameter, and the seed may become 
infected. Seedlings from such seed are stunted and the 
stand poor. Cankers occur on the stems of young plants. 
Seed should be taken only from healthy plants. Treatment 
of seed with concentrated sulfuric acid to remove the lint, 
followed by either the mercuric chlorid or the hot-water 
treatments may be employed to advantage. 

Damping-off (Pythium debaryanum and other fungi). — 
Young cotton plants may suffer the characteristic soft rot 
of damping-off. 

Sore-shin {Corticium vagum, Rhizodonia) . — Primarily 
this is an ulcerous wound upon the stem near the ground, 
accompanied by reddening or browning of the leaves. If 
the ulcer enters deep into the stem, so as to interfere with 
the ascending sap, it may cause death, though the wound 
usually heals before the disease has progressed far. The 
disease is often caused by the attack of Rhizoctonia, espe- 
cially^ in tissues predisposed to such attack by weakness. 
Harrowing, to aid in drying the surface soil, to some extent 
prevents the attack and development of this fungus. 

A similar disease may also result from purely mechanical 
injuries caused by tools. 

Smut {Doassansia gossypii Lag.) occurs on the leaves in 
Equador and the West Indies. Rust (Kuehneola gossypii 



350 Diseases of Economic Plants 

(Lag.) Arth.) is reported on the leaves from Florida, Cuba, 
Porto Rico, and British Guiana. Cluster-cup-rust {Mcidium 
gossypii E. & E.). — An outbreak of this disease occurred in 
southern Texas in 1917, causing large defoliation, with an 
estimated loss in yield of 20 per cent. It is commonly present 
in the South to a degree, but usually does not assume destruc- 
tive proportions. Crown-gall (Pseudomonas tumefaciens) 
does some injury. 

Mosaic, black-rust. — The first signs of this disease are 
yellowish spots which give the leaf a checkered appearance. 
The discoloration occurs first in small areas, which are 
roughly rectangular owing to limitation by the veins, and 
which are situated at points most remote from the main feed- 
ing veins. Usually the centers of these spots soon turn 
brown, and the brown part enlarges and shows a series of 
concentric markings. In later stages these weakened areas 
may be overgrown by Alternaria or other saprophytic fungi. 
If very dark-colored fungi grow upon these spots, they soon 
become black-coated and take the popular name ''black 
rust." 

Kainit, used as fertilizer, often reduces the damage from 
mosaic. 

Red leaf-blight. — This reddening, resembling autumnal 
coloration, occurs most frequently toward the season's end 
and is most common upon poor soil. It is due chiefly to 
lack of nourishment. 

Attack of mites produces a similar appearance. 

Shedding. — This occurs chiefly following extremes of 
either dry or wet weather or following a change from one ex- 
treme to the other. 

FLAX 

Wilt ^^^ {Fusarium lini Bolley) . — A condition of soil 
known as ''flax sick" has prevailed in many sections of the 
country to such an extent as to cause the abandonment of 
flax culture. This is notably true in Iowa, Minnesota, North 



Fiber Plants 351 

and South Dakota. On such soils flax plants are attacked at 
any age, and die early or late according to the time and in- 
tensity of the infection. Man}^ of the plants are killed before 
they appear above the surface of the ground. Such field 
spots become centers of disease; they enlarge throughout the 
summer, and new plants sicken, wilt, and die around their 
margins, finally giving the entire field a spotted appearance. 
Young plants wilt suddenly and dry up, or decay if the 
weather is moist. Older, woody plants become sickly and 
weak, turn yellow, wilt at the top, and die slowly. Such 
plants are easily pulled up, owing to their decayed root 
system. 

•Many of the roots of diseased plants are dead and have 
a characteristic ashen-gray color. If the plant is attacked 
late in the season, this gray color may be limited to one side 
only of the taproot. In such cases the leaves and branches 
on the affected side are blighted. If the disease is carried with 
the seed into healthy soil, only a few plants may be attacked 
during the first year, and such plants may be very unevenly 
scattered throughout the field and escape notice until late in 
the season. 

If the weather favors the disease, each new area of infesta- 
tion may increase sufficiently to reach plants in several 
adjacent drill rows. These infested areas are nearly al- 
ways circular, and enlarge each year that flax is grown 
thereon. Such a spot 1-2 m. in diameter the first year 
may become 2-3 m. the second year. Thus only a few years 
are required for the disease to gain complete possession of a 
field. The fungus not only persists in a field not sown to 
flax, but the disease areas may even enlarge when no flax is 
present. When soil is once infested, no way is known to 
render it again suitable for flax culture. 

This is essentially a soil disease, and it is spread in the 
ways suggested under soil diseases, notably by soil particles, 
drainage water, and especially by straw of diseased flax which 
may get into the manure. The chief agent of dissemina- 
tion, however, is the seed. In threshing, the spores of the 



352 Diseases of Economic Plants 

causal fungus, which are abundant upon the dead .straw, 
find lodgment upon the seed, especially if it be moist. 

To prevent carrying the disease to land yet uninfested, 
all seed should be disinfected in the following manner : 

Use formaldehyde at the rate of 1 pound to 40 or 45 gallons 
of water. Spread the seed upon a tight floor or upon a canvas 
and sprinkle or spray upon it a small amount of the liquid. 
Shovel, hoe, or rake the grain over rapidly. Repeat this 
spraying, shoveling, and raking until all of the seeds are 
evenly moistened, yet not wet enough to mat or gum to- 
gether. Continue to stir the grain, so that the mass may 
become dry as soon as possible. Avoid any excess of moisture. 
If flax seeds are dipped in the solution or are allowed to be- 
come wet enough to soften the coats so that they stick to- 
gether, they are liable to be considerably injured or even 
killed. 

The solution recommended is strong enough to kill all 
seeds if they are thoroughly saturated or are allowed to re- 
main damp for some hours. Less than one-half gallon of 
solution is required to treat one bushel of seed. It is well, 
also, to burn all the infested straw and to avoid too deep 
planting. 

By continued selection of seed from resistant plants 
Bolley has developed a variety which is resistant to the 
wilt. 

Damping-off of young plants may be caused by Alternaria 
or CoUetotrichum. 

Rust (Melampsora lint (DC.) Tul.). — Characteristic 
rust sori are in evidence and in the early season the leaves 
are yellow or orange. Later black sori appear, chiefly upon 
the stems. Badly affected plants turn l)rown and die earlier 
than plants not rusted. Large injury is not usual, though in 
1904 and 1905 considerable damage was reported from North 
Dakota. 

Dodder (Cuscuta epilimmi Weihe) is similar to the dodder 
of legumes. See alfalfa. 



Fiber Plants 353 

HEMP 

Wilt ^''' {Botryosphceria marconii (Cav.) C. & J., Dendro- 
phoma). — With the attack, appearing first upon the outer 
ends of the upper branches, the plant wilts rapidly. The 
foliage soon turns brown and dies. The disease seems to be a 
recent importation from China. 



TREES AND TIMBER ^'^^' ^^^ 
General Diseases 
DECAY IN LIVE TREES ^^^ ^^'^ 

Wood decay is caused by fungi. The mycelium penetrates 
through or between the wood cells, producing enzymes which 
soften the cells or disintegrate the middle laj^er between 
cells, thus destroying stability of the aggregate as by the 
crumbling of the plaster or the brick of a wall. Within 
the tree this disintegration may occur either to the heart- 
wood or to the sapwood, or to both. 

The life of a tree may be much reduced by decay of the 
heartwood, the main mechanical support. Decay of the 
sapwood further hastens death by interfering with the rise of 
the sap. 

Upon the living tree the natural protection against fun- 
gous invasion is the bark, consisting of cells with specially re- 
sistant walls; cutinized or supplied with resin, gum, or other 
repellents. Moreover, the dead bark is not generally nutri- 
tious and does not offer attractive invitation to the fungus. 
The protection thus constituted is normally ample; but in 
case of removal of this natural protection and exposure of 
either sapwood or heartwood, especially the latter, the path 
is open, and it is through wounds offering such exposure 
that rot in standing timber usually begins. Such rots might 
therefore be appropriately termed ^' wound decays." 

The fungi which cause these decays are, in the main, 
the larger fungi whose fructification is of the toadstool type 
(Figs. 191, 194). After the decay within is well under way 
the spore-bearing toadstools appear upon the surface of the 
diseased parts, and are quite generally recognized by lumber- 
men as a sign of rottenness within. 

354 



Trees and Timber 



355 



A branch, broken or sawed off, split by wind, bruised 
by a falling tree, gnawed by animals, pecked by birds. 




Fig. 184. — Fomes igniarius upon live beech tree 
After Atkinson. 



eaten by insects, or wounded in any way, may result in the 
exposure of heart or sapwood to the fungous spore. From 
this point of invasion rot spreads in every direction. When 
decay reaches the trunk, it spreads upward and downward 



356 



Diseases of Economic Plants 



and into all branches to which it has access. Thus trees, 
hollow with rot, may trace their downfall to infection of some 
small branch or bark wound months or even years earlier. 
Trees bearing the sporophores of fungi (conchs or toad- 




FiG. 185. — Stump of limb improperly removed. After 
Ind. Agr. Exp. Sta. 

stools) are surely infected, while the absence of su(;h evidence 
is no sign that a tree is healthy since the infection may be 
very old and the sporophore earlier in evidence may have 
rotted away. 

The fungi involved in these decays are manifold. In 
some cases one species of fungus grows upon many different 
kinds of wood. Other fungi are more particular as to their 



Trees and Timber 



357 



food supply and are found upon fewer hosts. They chiefly 
fall into two groups; one bearing its spores upon gills 
(Fig. 194); the other with its spores borne in pores. 
Still others bear their spores upon spines. In describing 
the fructification of the causal fungi for recognition pur- 
poses it is necessary to 
note especially the 
stalk or stiye, and the 
cap or pileus (Fig. 194). 
A cap with no stalk is 
''sessile." To deter- 
mine the particular 
species of fungus that 
is present, it is usually 
necessary to examine 
the sporophore, and 
even then expert or 
special knowledge is 
needed.* The deter- 
mination of the species 
of the fungus is, how- 
ever, not necessary to 
proper treatment, since 
this is much the same 
for all. 

Care should be ex- 
ercised in felling trees 
to avoid injuring other 
trees. In forests in 
general, cull material and infected standing trees should be 
burned to prevent spore formation. Excision of the infected 
tissue should be practiced in case of especially valuable trees. 
When there are pruning-wounds, apply an antiseptic to the 
exposed wound to prevent the effective germination of spores 
upon its surface. Suitable antiseptics are tar or paint. 

* Useful books in such classification are given in the bibhography, 
Nos. 381-387. 



M| 


mm-: 




^^H 


wm' .\; 


-,. 


^^^^H^9P 






^^Bk^'' 


F^ .'""'« 


, 


^^^c<« 


*'• •- 




jHMjg 


mi^i.- ' %.. . 


, \ 


^^^H 


H' /- 


'\^ 


r 






M':f: 


ihi / 


i 




>i\ 




1 






HiPv 


■^, 






i 


/> 


H j 


y 


\N ■ 


■Hi 


K. '^ " 


. .^m 



Fig. 186. — Wound of properly removed 
limb, beginning to heal over. After 
Ind. Agr. Exp. Sta. 



358 



Diseases of Economic Plants 



Red heart-rot, Pecky heart-rot ^^^ {Trametes pini Fr.) . — 
In the North this is the most destructive tree rot affecting 
practically all conifers, invading the heartwood, very rarely 
the sapwood. The wood is not wholly destroyed by the 




Fig. 187. — Wound of properly removed limb nicely healed 
After Ind. Agr. Exp. Sta. 



over. 



fungus; but series of small holes with silvery lining are noted 
in early stages. In spruce the color of the wood itself is 
changed to a light purplish gray, later to a reddish brown 
netted with small black lines. Small patches of white follow, 
which later develop into holes, arranged in series to corre- 



Trees and Timber 359 

spond with the annual rings, and as the disease progresses 
result in a series of vacant spaces separated only by plates. 
In tamarack the decay finally destroys the plates, reducing 
the v/hcle wood mass to mere fiber. 

The sporophores may consist either of brackets or of 
extended sheets with shallow, pit-like pores on the under 
side. They are cinnamon-brown on the lower surface and 
much fissured and broken on the black, charcoal-like upper 
surface. Prevention is best effected by proper thinning, 
removing diseased trees, and destroying fruiting bodies. 

White heart-rot "^^^ (Fomes igniarius Gill.). — This is the 
most important and widespread of the heart-rots, and one 
which has the widest range of host plants. It is known in 
Alaska, Canada, the United States, and in South America to 
Patagonia, growing upon beech, aspen, birch, poplar, willow, 
mountain maple, sugar maple, hornbeam, white elm, butter- 
nut, black walnut, oaks, and hickory. It is common on fruit 
trees, especially when near forests. The amount of damage 
done by it is beyond estimation. In many cases almost the 
entire tmiber stand is ruined. Actual count has shown from 
90 to 95 per cent of otherwise marketable trees valueless. 

Heart-rot, while chiefly of the heartwood, may, when 
started, encroach upon the sapwood, even to the youngest 
layers, and death may result by weakening the tree to the 
breaking point. The causal fungus enters through wounds, 
particularly broken stubs, and usually produces its sporo- 
phores at these points after the rot has extended a meter or so 
in both directions from the infection point. The first sure 
external sign of the disease is the presence of the sporophores, 
although sounding with the ax may sometimes be relied upon. 

The sporophores, numbering sometimes as many as 
twelve on a tree, are shelving, hoof-shaped bodies from 
25 to 30 cm. wide. The upper surface is brown, in later 
stages black, hard, smooth, concentrically marked with 
age, finally seamed and cracked. The pores are in layers, 
approximately annual, and the lower surface is gray to red- 
brown. 



360 



Diseases of Economic Plants 



The trunk in cross-section shows rot at the center; the 
wood becomes soft and pulpy. The decayed region is ir- 




FiG. 188. — Fomes igniarius upon maple. After von Schrenk. 



regular in outline and bounded by narrow black layers. The 
tree is rarely hollow, but remains filled with the decayed 
wood. Young trees which bear no dead branches to admit 
the fungus are usually immune. 



Trees and Timber 361 

Infective material should be burned, wounds avoided, 
and excision practiced in case of valuable trees. 

Red heart-rot, Brown-checked wood-rot ^^^' ^^^ (Polyporus 
sulphureus Fr.). — The conifers, also oak, chestnut, maple, 
walnut, butternut, alder, locust, apple, pear, cherry, and 
many other trees are affected. It is widely distributed, de- 
structive, and is especially common on shade and ornamental 
trees. 

The many-pored edible annual sporophores consist of a 
series of overlapping shelves, two to twenty or possibly more, 
with the upper surface in early stages a bright orange-red; 
later they are sulphur-yellow both above and below. The 
upper surface when bruised is brown. The sporophore is 
soft and fleshy when young, growing hard and brittle with 
age. This fungus abounds on knots and stumps. The rotted 
wood resembles red-brown charcoal and following decay 
bears concentric and radial cracks due to shrinkage. In these 
cracks are large sheets of fungous wefts. 

Diseased trees should be cut and burned to prevent 
infection. 

Piped-rot (Polyporus sps.). — The oak, chestnut, beech, 
and birch are susceptible to this rot, which is limited to the 
heart wood and is characterized by irregular, small, pocket- 
like patches of white fiber. These regions first appear in the 
wood as small, lenticular areas which increase, coalesce, and 
change into small pockets. These frequently become filled 
with a dark, red-brown mycelium. The speckled character 
of the wood is a distinctive mark. 

White-rot {Hydnum erinaceus Bull.). — Although ob- 
served upon many kinds of trees, oaks are chiefly affected. 
The rotted wood is soft and wet, with numerous holes full of 
light yellow floccose mycelium. The fleshy sporophores are 
white, 1 to 25-30 cm. in diameter, nearly spherical, and 
consist chiefly of immense numbers of white spines upon 
whose surfaces the spores are borne. 

Heart-rot ^'^^ {Fomes fidvus Gill.). — In Missouri and 
Arkansas this heart-rot is found upon birch and a number of 



362 



Diseases of Economic Plants 



other trees. The wood turns brown, and crumbles under 
pressure. The rot extends from 3-4 m. above and below the 
sporophores. These are pore-bearing, triangular in section. 




Fig. 189. — Polyporus sulphureus showing effect upon wood of oak 
tree. After von Schrenk. 



The upper surface is very hard and bears fine, irregular 
fissures parallel to the edge. When mature, the upper 
surface is red-brown. The pores are barely visible without 
a hand lens. 

Soft-rot ^^^ {Polyporus obtusus Berk.). — The black oaks 



Trees and Timber 



363 



{Q. marylandica and Q. velutina) are chiefly affected by this 
rot, which is found in Missouri, Arkansas, Iowa, Tennessee, 
Mississippi, New Jersey, and Maryland. 




Fig. 190. — • Tree weakened by Fomes fomentarius. 
After Atkinson. 



The causal fungus enters through the burrows of a wood 
borer. The heartwood turns light yellow, then white, 
and becomes brittle. Strings and sheets of white mycelium 



364 



Diseases of Economic Plants 



are found in the wood. Death results either from diminu- 
tion of water supply or from breaking of the trunk. 

Heart-rot, White wood-rot ^^^ (Fomes everhartii (E. & G.) 
Schr.). — This closely resembles the rot produced by 
Fomes igniarius. Large, rusty-brown, woody sporophores, 

red-brown below, grow 
from wounds and 
bear very small pores. 
White-rot ^^' (Poly- 
porus squarnosus Fr.). 
— In Europe this rot 
affects pear, oak, elm, 
walnut, linden, wil- 
low, ash, birch, beech, 
horse-chestnut, and 
maple. In America it 
has been reported from 
Minnesota. The wood 
becomes unusually 
white and bears scat- 
tered series of white 
lines. 

The nearly circular 
fruiting bodies are 
stalked and often at- 
tain a diameter of 
15 cm. When young, 
they are soft, but 
later become very 
scaly and rough. 

Gill.).— This rot 




Fig. 191. — • Fomes fomentarius showing 
hoof-shaped sporophore. After Atkin- 
son. 



tough. The upper surface is 

Sapwood rot ^^^ (Fomes fomentarius 
abounds throughout the northern part of the United States, 
as one of the most common diseases of deciduous trees, 
chiefly affecting the beech and birch. 

Decay begins in the outer sapwood and proceeds in- 
ward. The wood is marked by irregular black lines, the 
boundaries between diseased and normal wood. When en- 



Trees and Timber 



365 



tirely rotten, the wood is soft and spongy and light yellow 
in color. 

The pore-bearing sporophores are hoof-shaped, smooth 
above, and concen- 
trically ridged and 
gray. Below they 
are red-brown. 

Rot {Forties ap- 
planatus Wallr.). — 
The shelving, per- 
ennial, pore- bear- 
ing sporophores are 
very large, woody, 
and grayish to 
brown above, and 
are commonly 
found on dead 
wood, as well as 
on live trees of 
poplar, beech, oak, 
birch, maple. 

Red-brown rot^^^ 
" (F omes pinicola 
Fr.). — The causal 
fungus is of world- 
wide distribution 
upon conifers, 
especially spruce, 
pine, fir, and hemlock. It occurs also upon birches and 
other deciduous trees. Entrance is made through wounds. 
The rotted wood is brittle, cracked, and permeated by 
numerous sheets of mycelium. In early stages of decay 
the color changes from red-brown to dark-brown, after 
which small, irregular, scattered white areas appear. The 
sporophores vary from 2.5-30 cm., averaging 10-15 cm., 
are bracket-shaped and lobed. The young lobes are 
bright red to pale yellow, old ones dark red-brown. 




Fig. 



192. — Fomes applanatus upon trunk of 
dead tree. After Freeman. 



366 



Diseases of Economic Plants 




Fig. 193. — Fruiting body of Fomes pinicola upon log rotted 
by the fungus. After von Schrenk. 



Trees and Timber 



367 



The lower surface is pale and smooth, watery when 
bruised. 

Following is a list of the principal genera of wood-rotting 
fungi with the names of the trees on which they grow. Such 
as bear page references are discussed on the pages indicated. 



Fungus 

Armillaria, p. 370. 
CoUybia. 

Daedalea. 
Echinodontium. 
Favolus. 
Fistulina. 
Fomes, pp. 359, 
364. 



Hydnum, p. 361. 

Irpex. 

Lentinus. 

Lenzites. 

Pholiota. 
Pleurotus. 

Pluteus. 
Polyporus, p. 361. 



Hosts 

Oak, apple, and trees in general. 

Horse-chestnut and deciduous trees gen- 
erally. 

Chestnut, maple, oak. 

Fir, hemlock, p. 389, spruce. 

Deciduous trees. 

Chestnut, oak. 

Alder, apple, arbor-vitae, ash, p. 381, as- 
pen, balsam, beech, birch, butternut, 
Cottonwood, currant, cypress, elm, fir, 
goose})erry, hemlock, hickory, juniper, 
p. 383, larch, locust, p. 391, maple, oak, 
olive, orange, peach, pine, plum, poplar, 
rose, sassafras, p. 402, spruce, syca- 
more, walnut, willow, and conifers and 
deciduous trees generally. 

Apple, beech, maple, oak, spruce, and 
deciduous trees generally. 

Trees generally. 

Aspen, birch, pine, poplar. 

Beech, fir, pine, poplar, spruce, and coni- 
fers and deciduous trees generally. 

Apple, oak, poplar, and trees generally. 

Elm, fir, maple, mulberry, pine, poplar, 
willow. 

Deciduous trees generally. 

Alder, apple, arbor-vitae, ash, balsam, 
beech, birch, p. 382, butternut, catalpa, 
p. 382, cedar, cherry, chestnut, elm, fir, 



368 



Diseases of Economic Plants 



Polystictus. 
Poria. 

Schizophyllum. 

Septobasidium. 

Steccherinum. 

Stereum. 

Thelephora. 
Trametes, p. 358. 

Tricholoma. 
Volvaria. 



hemlock, juniper, p. 384, larch, linden, 
locust, maple, oak, orange, pear, pine, 
poplar, Pseudotsuga, spruce, walnut, 
willow, and conifers and deciduous 
trees generally. 

Ash, catalpa, mountain ash, and decid- 
uous trees generally. 

Birch, catalpa, fir, hemlock, juniper, pine, 
spruce, and conifers and deciduous 
trees generally. 

Chestnut, horse-chestnut, mulberry, and 
many other trees. 

Apple, oak, palmetto, tupelo, etc. 

White cedar (ChamcBcyparis) . 

Birch, larch, oak, poplar, willow, and 
drupes and pomes. 

Oak and trees generally. 

Birch, fir, hemlock, larch, locust, pine, 
spruce, willow. 

Deciduous trees. 

Trees generally. 



Canker, gall, twig-blight. — These diseases occur upon 
nearly all kinds of trees. Galls are swollen parts, of the 
general character illustrated in Figs. 44-212. Cankers are 
bark diseases of varied extent (Figs. 10, 14). Twig-blight 
consists of death of a twig through disease (Figs. 30, 214). 
When occurring on valuable trees, excision or spraying may 
be warranted, but on forest trees, manifestly no such treat- 
ment is possible, and the only recourse is to adopt general 
sanitary measures, particularly the burning of infective 
material. 

The principal causes of these diseases with the hosts are 
given below. Those with page references are given more 
complete discussion on the pages indicated.* 

* References to books where descriptions of these fiingi may be found 
are given in the bibliography under numbers 390-394. 



Fungus 
Ascochyta. 
Bacteria. 



Botr3rtis. 

Cenangium. 

Cronartium. 

Cryptosporella. 

Cyanospora. 

Cytospora. 

Dasyscypha. 

Diaporthe. 

Diplodia. 

Dothidea. 

Dothichiza. 

Dothiorella. 

Endothia. 

Gymnosporan- 

gium. 
Mjrxosporium. 

Nectria. 



Trees and Timber 

Hosts 



369 



Nummularia. 
Phoma and 

Phyllosticta. 
Physalospora 

(Sphaeropsis). 
Pseudomonas 

tumefaciens. 
Strumella. 
Valsa. 



Spruce. 

Filbert, p. 389, mountain ash, mulberry, 
p. 393, oleander, olive, pomes, poplar, 
walnut, p. 404. 

Fir, hemlock, horse-chestnut, larch, linden, 
orange, pine, Prunus, spruce, sycamore. 

Pine. 

Pine, p. 395. 

Hazel, p. 389. 

Juniper. 

Chestnut, maple, mulberry, poplar, p. 401, 
willow. 

Hemlock, p. 390, larch, pine, spruce. 

Dogwood, fir. 

Oak, p. 394. 

Oak. 

Cottonwood, poplar, p. 401. 

Walnut, p. 404. 

Chestnut, p. 396. 

Cupressus, incense cedar (Libocedrus) , 
white cedar (Chamcecy parts), juniper. 

Apple, beech, conifers, oak, pear, syca- 
more, tulip. 

Alder, apple, arbor-vitse, ash, beech, 
birch, box elder, China berry, cherry, 
dogwood, elm, fir, hazel, horse-chestnut, 
linden, maple, mulberry, oak, pine, 
spruce, walnut, and conifers generally. 

Mountain ash, pomes. 

Apple, juniper, p. 385, pine. 

Birch, chestnut, oak, willow, fir, pomes, 

mulberry, elm, magnolia. 
Apple, chestnut, oleander, peach, pecan, 

poplar, quince, spruce, willow. 
Chestnut, oak. 
Alder, apple. 



370 



. Diseases of Economic Plants 



ROOT-ROTS 

Fungi similar to those that cause wood-rot may also at- 
tack the roots of trees and thus cause death either with or 
without any previous rotting of the trunk wood. Prominent 
among such diseases are the following: 

Shoe-string root-rot ^^^ (Armillaria mellea Vahl). — The 
fungus usually enters the root through wounds, and grows in 




Fig. 194. — Armillaria mellea attackmg a tree. After Freeman. 

the cambium, through which it spreads until it encircles 
the tree. As its growth proceeds the layers adjacent to the 
cambium become dry, and the top of the tree is killed by 
stoppage of its water supply. A characteristic accompani- 
ment is the profuse development of string-like, hard, black 
mycelial strands which permeate the soil near the base of 
the affected tree. From the mycelium around the base 



Trees and Timber 371 

of the tree rise the numerous white-gilled, honey-colored 
sporophores, their viscid tops flecked with white; the stems 
swollen and with a ring (annulus) . 

This disease may spread for long distances through the 
soil by means of the fine roots and infect neighboring trees. 
Upon newly cleared land diseased roots of forest trees may 
be a source of infection to fruit trees subsequently grown 
thereon. The disease is common to both conifers and de- 
ciduous trees and has been particularly troublesome on oak, 
pine, chestnut, larch, sycamore, poplar, locust, hemlock, 
birch, alder, maple, and orchard trees. 

Red-rot ^^^ (Fomes annosus Fr.). — Though not very de- 
structive in this country, this fungus has been found on 
pine, spruce, fir, and other conifers, more rarely on deciduous 
trees, where it brings about a brown or red-rot of the root 
system, which ultimately results in the death of an affected 
tree. The fruiting bodies form small, cup-shaped shelving 
or irregular masses on the roots or around the base of the 
trunk. The fungus has also been found growing on old, dead 
trees. Neighboring trees generally become infected from a 
diseased tree, through the small fil^rous roots. 

Red-brown Root-rot ^^^ {Polyporus sckweinitzii Fr.). — 
A destructive root-rot of spruce, fir, arbor-vitse, hemlock, 
larch, and pine, by weakening the root or trunk, leads to the 
overthrow of the tree by wind. 

The point of attack is always the root, through the heart 
of which invasion is made into the trunk. This often leads 
to one-sided decay of the trunk's heartwood. The wood is 
rendered brittle, yellow, and later of cheese-like character, 
so that it can readily be cut cross grain when wet or reduced 
to a powder when dry. 

The pore-bearing sporophores, which appear in July or 
August, are from 10-35 cm. across, growing either from the 
roots or the trunk. If from the trunk, they are sessile; 
from the roots they are stalked. The fresh spore layer is rose- 
colored, and turns dark red if bruised. 

This disease is very common throughout northern for- 



372 



Diseases of Economic Plants 



ests. In Europe, where it is greatly dreaded, it is customary 
to prevent its spread by trenching. Groups of infected trees 
and trees near them may be cut to advantage to protect other 
trees. Other toadstool fungi that cause root-rot are Cli- 




FiG. 195. — Log rotted by Polyporus schweinitzii. After von Schrenk. 



tocybe, Tricholoma, and Septobasidium. Root-rots are also 
due to other fungi, chiefly the following: 

Ozonium Root-rot {Ozonium omnivorum Sh.). — Elm, 
basswood, oak, cottonwood, mesquite, china tree, mulberry, 
apple, and pear are affected by this rot, which has been de- 
scribed and discussed on page 23. 



Trees and Timber 



373 



Rhizina on fir, pine, larch, spruce, hemlock, Pseudotsuga, 
chestnut; Sparassis on fir, spruce, pine, larch; and Thielavia 
(see p. 23) on catalpa; Xylaria, see p. 53. 



DECAY OF DEAD TREES OR DEAD PARTS 

While decay of dead trees cannot be regarded strictly 
as a condition of disease, but rather as a post-mortem 




Fig, 196. — Dry-rot fungus (Merulius lacrymans) ; on the right the 
mycelium is visible as white strings. After Freeman. 

change, a word is due on account of its vast importance, 
involving, as it does, all structural wood. The fact that 
the railroads purchased 121,402,611 cross-ties in the year 
1915, and larger numbers in preceding years; that the num- 
ber of posts in use in 1910 was approximately 4,000,000,000, 



374 Diseases of Economic Plants 

necessitating an annual replacement of some 500,000,000 
in the United States, indicates the enormous money values 
involved. 

Decay of timber is brought about by agencies similar, 
sometimes identical, with those causing rot in living trees, 
but cannot occur unless both moisture and oxygen are avail- 
able. Decay can be prevented by impregnating the wood 
with various antiseptics, as creosote or zinc chloride. ^^^' ^^^ 
Merely removing the bark from posts increases their length 
of utility. 

A few of the chief causes of the decay of dead wood are as 
follows : 

Dry-rot {Merulius lacrymans (Jcq.) Fr.). — One of the 
most common and destructive of all the rots of structural 
timber, it renders the wood spongy and brownish. If very 
moist, a profuse, superficial, pure white mycelium may 
develop, at first loosely, later in dense sheets or strands. 
The sporophores are flat, at first white, later red, and still 
later yellow-brown. The spore-bearing surface carries 
shallow pores penned between folds and wrinkles. 

Sap-rot ^^^ (Polyporus versicolor Fr.). — In addition to 
its parasitic life upon the chestnut and catalpa, this fungus 
grows as a saprophyte upon all kinds of deciduous woods, 
and is regarded as the most serious of all wood-rotting 
fungi which attack the dead wood of broad-leaf trees. It 
destroys probably 75 per cent or more of the broad-leaf 
species of timber used for tie purposes. Whenever such 
species are used for fencing, for posts or poles, or for any pur- 
pose where they come in contact with the soil, they are sure 
to be attacked sooner or later by P. versicolor. P. -per game- 
nus Fr is similar to P. versicolor, and also of great im- 
portance, appearing upon cut timber or on large wounded 
surfaces of standing trees, especially following fires. It 
is found throughout the United States on all deciduous 
woods. 

Numerous genera and species of fungi other than those 
mentioned above can also bring about similar changes. 



Trees and Timber 



375 



MisiXeioe ^^'^ {Phoradendron and Razoumofskya) . — While 
not generally considered pests, these parasites under favora- 
ble weather conditions may become so, especially upon trees 




I'iG. 197. — Trees intcstetl with mistletoe. Courtesy of the School 
of Botany of the University of Texas. 

in lawns and parks. They usually attack the smaller branches 
of the trees, and thus cut off the nourishment from their 
tips and eventually cause these portions to die. The general 
effect is to spoil the beauty of the tree. On forest trees they 
cause small diameters, reduced height, and scraggy crowns. 



376 Diseases of Economic Plants 

To destroy mistletoe the infected branches should be cut 
from the trees and no berries allowed to mature, thus pre- 
venting dissemination of the pest by birds. Razoumofskya, 
the dwarf mistletoe, is represented by some eleven species in 
the United States, parasitic on conifers, spruce, pine, fir, 
hemlock, larch. Phoradendron, or the leafy mistletoe, 
consisting of several species is found on practically all kinds of 
broad-leaf trees. 

Witches-brooms. — The production of numerous adven- 
titious buds may result in the close, broomlike branching 
which gives rise to this common name. The condition is 
prevalent on many kinds of trees, particularly so on the hack- 
berry, which is rarely without the witches-brooms in profu- 
sion. They are also common on horse-chestnut, juniper, and 
fir. The cause of this abnormal branching is a stimulus im- 
parted by insects (mites), or by any one of several fungi as for 
example: Taphrina, Gymnosporangium, Peridermium, or 
the Powdery-mildews. 

Slime-fiux. — This is a term applied to a condition in 
which portions of the tree are covered by a slimy, fermenting, 
wet, often foamy, flow. This usually originates in sap oozing 
from a crack or other wound, often following surgical work, 
and is most in evidence when the sap flows freely. The 
organisms, yeast, bacteria, or their products, that induce the 
fermentation, may cause death of neighboring cells of the 
tree and result in a chronic wound, though the injury is at 
rn.ost little more than unsightly. Excision and disinfection 
niay be practiced. 

' Damping-off ^^' ^^' ^^^ {Corticium, Pythium, and Fusa- 
rium). — Coniferous seedlings chiefly are affected. Soil 
disinfection by sulfuric acid, copper sulfate, zinc chlorid, or 
formalin, or when practicable by steam, are advised. See 
p. 460. 

Tree Surgery '^^^ ^o^, 403, 378 

Ornamental, shade, and even nut and fruit trees are often 
of value sufficient to warrant careful surgical treatment to 



Trees and Timber 



377 



prevent further inroads by 
fungi already established 
in them. The real value 
of surgical treatments is 
somewhat problematical. 
The practice is of compar- 
atively recent popularity, 
and a long interval of time 
is necessary to determine 
the amount of benefit. 
The procedure is as fol- 
lows: First, all decayed, 
diseased, or injured wood 
or bark must be removed, 
either by severing a limb 
entire or by cutting out 
a cavity, in which case 
a mallet, sharp gouges, 
chisels, and a knife are 
needed. To reach all of 
the diseased wood it is 
usually necessary to en- 
large the opening and fre- 
quently to make one or 
more holes above or be- 
low the main opening, or, 
what is perhaps better, to 
cut a narrow opening of 
the required length. The 
excavation should be en- 
larged in all directions 
until only sound, unin- 
fected wood is left. The 
bottom of the cavity 
should be so shaped as 
to provide drainage. The 
edges of the cavity should 




Fig. 198. — • Detailed view of exca- 
vated and bolted cavities. Above 
cross-section of a young tree trunk 
showing how the new wood and 
bark grow into an unfilled cavity 
from the margin. (The line on the 
wood indicates the amount of ex- 
cavating that would be needed be- 
fore filling the cavity.) 3. — ■ Cross- 
section of a tree trunk showing 
the manner of using two single- 
headed bolts to brace a cavit}'-. 
After Collins. 



378 



Diseases of Economic Plants 



be undercut so that the filling will be held firmly in place, 
but, lest they dry out, should not be less than three- 
quarters of an inch thick, better an inch and a half. If 
there is but little undercutting, nails may be driven into 
the interior to hold the filling. The final cutting around 
the cambium should be made with a sharp knife and imme- 
diately followed by a coating of shellac covering the edges 
of the cambium, bark, and sap wood. In cavities more than 
two feet long, it may be necessary to reinforce the remaining 
wood by bolts placed every 18 to 24 inches at appropriate 
angles. After excision is completed, the entire inner surface 




Fig. 199. — Least objectionable method of an- 
choring guy wires to trees. After Stone, 

should be disinfected with creosote or carbolineum, and over 
this a heavy coating of tar or hot asphalt applied. 

The cavity may then be filled, using Portland cement and 
sand (1 to 3) well tamped in, the cement being put in to form 
blocks about 12 inches high and separated by tarred roofing 
paper. The face of the cement should be trimmed back to 
the level of the cambium. Instead of filling the cavity with 
cement, a mixture of dry sawdust and* asphaltum, 3 or 4 
parts to 1, may be used, with the advantage of greater 
elasticity to meet the winds. Or the cavity may be left un- 
filled and simply covered with a concrete layer with ap- 
parently equal advantages and much saving of cement. 
Metal coverings of tin or zinc are sometimes used, but in 
general are not so desirable. Shallow cavities are merely 



Trees and Timber 379 

excavated and disinfected and left without filling. Tree 
surgery should be done in mild weather, when the sap is not 
running actively. 

The necessity of surgical work can largely be avoided by 
early attention to wounds and especially by avoidance of 
wounds, and by the use of proper tree protectors and care in 
guying and staying branches to prevent galling or constric- 
tion. 

Leaf-spots, flower-blight. Numerous fungi cause spotting 
of leaves or disease of flowers of trees. These injuries are 
in general similar to leaf-spot, for example of celery, tomato, 
and other crops discussed on preceding pages. Ordinarily the 
injury in forests is not large, and treatment or even sanitary 
measures are out of the question. In the case of valuable 
shade, nut, fruit, or ornamental trees, or of nursery stock, 
spraying or dusting with fungicide is often advisable. Only 
the more important of the tree leaf diseases are discussed 
below. 

Following is a list of many of the fungi of leaf and flower 
diseases of trees with the hosts they most commonly infect. 
Page references are to further mention in other parts of this 
book.* 

Fungus Hosts 

Acantho stigma. Hemlock and conifers generally. 

Ascochyta. Butternut, oak, walnut. 

Asterina. Magnolia, oak. 

Cercospora. Ash, butternut, catalpa, linden, p. 391, 

maple, pecan, red-bud, sequoia, willow. 
CoUetotrichum. Magnolia. 
Cylindrosporium. Alder, ash, birch, elm, hackberry, locust, 

maple, walnut. 
Didymosphaeria. Catalpa. 
Entomosporium. Hawthorn. 
Fusicladium. Pecan, p. 394. 

* Books to aid in the study of these fungi are listed in the bibliography 
under numbers 390-394. 



380 



Diseases of Economic Plants 



Gloeosporium. 



Gnomonia. 
Gnomoniella. 
Hendersonia. 
Herpotrichia. 

Hypoderma. 

Keithia. 

Leptostroma. 

Leptothyrium. 

Lophodermium. 

Macrosporium. 

Marssonina. 



Microstroma. 

Monochagtia. 

Neopeckia. 

Peridermium. 

Pestalozzia. 

Phleospora. 

Phoma. 

Phyllosticta. 



Piggotia. 

Ramularia. 

Rhytisma. 

Rust (Uredinales) 



Septogloeum. 



Ash, beech, birch, butternut, hazel, hick- 
ory, horse-chestnut, Unden, maple, 
p. 392, oak, pecan, p. 395, sycamore, 
willow. 

Elm, p. 388. 

Hazel. 

Pine. 

Fir, incense cedar, larch, spruce, and 
conifers generally. 

Larch, pine, p. 397, conifers. 

Arbor-vitse, hemlock. 

Locust. 

Oak. 

Fir, juniper, larch, pine, p. 398, spruce. 

Catalpa, hackberry. 

Ash, butternut, p. 382, chestnut, p. 388, 
hickory, oak, poplar, p. 402, walnut, 
willow. 

Hickory, walnut, Inga. 

Chestnut, p. 388, oak. 

Pine. 

Fir, hemlock, pine, p. 401, spruce. 

Oak, spruce, and conifers generally. 

Elm, hackberry, sycamore, walnut. 

Fir, pine. 

Ash, beech, catalpa, p. 382, chestnut, 
elm, hackberry, hickory, horse-chest- 
nut, p. 390, linden, maple, p. 392, oak, 
poplar, sycamore, willow. 

Ash. 

Ash, hackberry, willow. 

Maple, p. 392, oak, willow. 

Ash, p. 381, birch, p. 382, cottonwood, 
fir, larch, mountain ash, osage orange, 
p. 394, pine, p. 395, poplar, p. 401, 
shadbush, willow, p. 405, 

Willow. 



Trees and Timber 381 

Septoria. Alder, ash, birch, chestnut, dogwood, 

hackberrj^, maple, oak, pine, poplar, 
sweetgum, sycamore, walnut, willow. 

Stigmatea. Juniper, sequoia. 

Taphrina. Alder, birch, elm, hornbeam, horse-chest- 

nut, maple, oak, p. 394, poplar. 

Venturia. Ash, birch, mountain ash, poplar, willow. 

Powdery-mildews. — The general character of these dis- 
eases and modes of treatment are discussed on p. 122. The re- 
marks made above regarding leaf-spot apply to the powdery- 
mildews as well. The chief trees on which they occur are: 
alder, ash, beech, birch, butternut, catalpa, chestnut, dog- 
wood, elder, elm, hackberry, hickory, horse-chestnut, honey- 
locust, linden, locust, maple, mulberry, oak, p. 394, pecan, 
p. 394, poplar, shadbush, sycamore, walnut, willow. 

Special Hosts 
ASH 

White-rot ^^^ {Fomes fraxinophilus Peck) . — In certain 
localities in Missouri, Iowa, Oklahoma, Nebraska, and Kan- 
sas this disease affects 90 per cent of the trees. It prevails in 
the Mississippi valley and east to the Atlantic. The heart- 
wood first darkens, and later becomes soft, pulpy, and yel- 
lowish. The shelving, pored sporophores, 5-10 cm. long 
and nearly triangular in section, are numerous, chiefly 
near stubs or wounds, appearing soon after infection. The 
old, upper surface is brown or black, and very hard. Trees 
of any age are susceptible, but those over 10 cm. in diameter 
are most subject to attack. Diseased trees should be cut 
down, or excision practiced. 

Rust {Puccinia fraxinata (Lk.) Arth.). — This is a rust 
which may be recognized by the orange-colored cluster-cups 
upon the swollen parts of the leaves and petioles of nearly 
all species of ash. The winter condition is found upon 
marsh-grass, Spartina. Usually the injury is not large, but 
in seasons favorable to the disease defoliation may result. 



382 Diseases of Economic Plants 

ASPEN. See poplar. 

BIRCH 

Sapwood-rot ^^^ {Polyporus betuUnus Fr.). — Several 
species of birch are affected by this rot, which is of wide 
distribution in the northern United States. The fungus en- 
ters the sapwood from the bark through wounds or through 
the lenticels, and progresses inward. When completely de- 
cayed the yellowish, cracked, diseased wood crumbles. 

Rust {Melampsoridium betulince (Schm.) Arth.). — This is 
much like the willow rust. See p. 405. 

BUCKEYE. See p. 390. 

BUTTERNUT 

Anthracnose {Gnomonia leptostyla (Fr.) C. & de Not. 
Marssonina). — The affected leaflets bear circular, dead, 
indefinitely bordered spots. The disease spreads very 
rapidly throughout the tree, and to other trees. Defoliation 
results. 

CATALPA 

Leaf-spot {Phyllostida catalpce E. & M.). — Affected 
leaves bear round, brown spots, often with a yellowish 
gray border. The spots, from 3-6 nmi. in diameter, often 
coalesce to form large blotches which are fragile, sometimes 
dropping from the leaf. Young leaves develop poorly and 
are deformed, while severe infection may cause complete 
defoliation of the tree. 

Soft heart-rot ""^^ (Polyporus versicolor Fr.). — The wood 
at the center of the tree is discolored and disintegrated, 
eventually becoming straw-colored and soft. The sporo- 
phores appear near the wound which afforded entrance. 
They are sessile, grouped, soft, hairy above with alternate 
bands of light and dark color. When old, they are tough 
with edges curled in. See also p. 374. 



Trees and Timber 383 

CEDAR, RED (Juniperus) 

Rusts ^*^^ {Gymnosporangium sps.). — Several distinct 
species of the parasite occur on Juniperus, some of which 
produce the usual "cedar-apples/' others produce cankers or 
witches-brooms on the branches, or spots on the leaves. 
They are usually of but small significance to the cedar tree 
itself unless exceptionally abundant. See apple rust. 




Fig. 200. — "Cedar-apple," gall of the rust fungus. Original. 

White-rot ^^"^ {Fomes juniperinus v. Sch.). — In this dis- 
ease holes appear in the heartwood, extending longitudinally 
with a partition of sound wood between. These cavities 
eventually may unite to form tubes throughout the tree. 
The wood between one cavity and the next is not the normal 
red, but is somewhat browned, and the holes themselves are 
coated with a brilliant white lining. The cavities, partially 
filled with a velvety reddish-yellow mycelium, may be from 
4-9 cm. long. The pore-bearing sporophore is hard and 



384 



Diseases of Economic Plants 



woody, rough above, later fissured, yellow-brown at the 
margin, later deep brown. The pore layer is yellow to 
brown. 

Red-rot, pecky-cedar ""^^ (Polyporus roseus Fr.). — More 
common than white rot, this has been observed in Missouri, 




"!C.JSi^ 



Fig. 201. — Cross-cut of cedar log showing effect of 
Fomes juniperinus. After von Schrenk. 



Arkansas, Kentucky, Tennessee, Virginia, New York, and 
Mississippi. 

The wood is full of pockets of brown, brittle wood, vary- 
ing from a centimeter to a meter or so in length. The sporo- 



Trees and Timber 



385 



phore, formed in the cavities under dead branches, is from 
0.5-35 cm. in length by 1 cm. wide. The pore-bearing layer 
is flesh-colored. 

This and the preceding disease of the cedar taken together 
have been estimated to cause 60 per cent loss in some local- 




FiG. 202. — Longitudinal section of cedar showing effect of Fomea 
juniperinus. After von Schrenk. 



ities. Since they are caused by wound parasites, the removal 
of diseased trees and the destruction of sporophores is 
recommended. 

Cedar canker (Phoma sp.). — This canker is found on 
juniper and arbor- vitae. Injury apparently occurs only on 
trees under four years old. Prior to that age entire seed beds 
may be destroyed. 



386 



Diseases of Economic Plants 



CHESTNUT 

Bark-disease ^"^' ^^' ^^^ (Endothia parasitica (Murrill) A. & 
A.). — First noted in 1904 by Merkel in New York, this 

disease has spread 
with a rapidity and 
destructiveness with- 
out parallel in plant 
pathology. Its dis- 
tribution in 1918 is 
indicated in Fig. 205. 
The disease extended 
by natural agencies 





Fig. 203. — Chestnut-bark disease. 
Beattie. 



After 



Fig. 204. — Chestnut- 
bark disease, show- 
ing the sporiferous 
pustules. After U. 
S. Bur. PI. Ind. 



through the native chestnut forests from Maine to Vir- 
ginia, but shipments of nursery stock have been responsi- 



Trees and Timber 



387 



ble for its spread to distant points, to British Columbia, 
California, Nebraska, etc. In most of these new, distant 
foci, the disease has since been eradicated. In Brooklyn 
16,695 trees were killed on 350 acres, and the loss in and 
about New York City in 1908 was placed at from $5,000,000 
to $10,000,000. The total damage prior to the year 1911 is 
conservatively placed at $25,000,000, and may now aggregate 




• *?oT /nrfc riots 
'I III tfVt^Al. IMffc r/o/¥S 

.^.-^ PMNse or eMtir«,u 



Fig. 205. — Distribution of chestnut blight in 1918. 
Office of Forest Pathology. 



Courtesy of the 



twice that amount, but this is insignificant compared with 
the loss that will ensue in the chestnut forests of the Appala- 
chians. It has already caused more damage to forest trees in 
America than any other fungus. The same disease has been 
found in China, and it is reasonably certain that it was intro- 
duced into the United States from the Orient some time prior 
to 1904. This pest is vigorously parasitic on members of the 
genus Castanea alone, and among the species of this genus the 
Japanese and Chinese varieties are highly resistant. The 
attack occurs upon the bark through wounds, Init twigs and 
leaves are not directly affected. From the point of attack 



388 Diseases of Economic Plants 

it spreads in all directions until the diseased parts meet on 
the opposite side of the branch, thus girdling the twig. Dead, 
discolored, sunken patches with numerous yellow, orange, 
or reddish-brown pustules are produced; spores are extruded 
in greenish or yellow horns. Cankers in midsummer may en- 
large at the rate of a half-inch in diameter each week. The 
appearance of the fungus upon the trunk indicates speedy 
death, but if small branches are first diseased, the tree may 
continue to live for a few years. When once established, no 
means of checking this blight is known. Only preventive 
measures can be taken, such as destruction of diseased trees 
by fire, careful inspection of all nursery stock, and excision 
in the case of isolated trees which are considered valuable 
enough to justify this mode of treatment. Every general 
measure that has been tried has been abandoned, and at 
present the outlook indicates that the disease will eventually 
exterminate the American chestnut. To the present time 
$165,000 has been used by Federal appropriation and 
$282,500 by states, $275,000 by Pennsylvania alone, in com- 
bating this disease. 

Anthracnose, leaf-spot {Marssonina ochroleuca B. & C). — ' 
The characters of this disease are small bleached areas bear- 
ing spore pustules. It has been quite injurious to nursery 
varieties. 

Bordeaux mixture is advised. 

Large leaf-spot (Monochetia desmazierii Sacc). — This 
leaf-spot is abundant in forests, and causes much loss of 
vigor to the tree. It is recognized as large, 1-5 cm., circular 
spots with irregular concentric marking. No treatment is 
feasible in forests, but isolated trees can be protected by 
spraying. 

ELM 

Leaf-Spot ^^^ {Gnomonia ulmea (Schw.) Thm.). — The leaf 
spots are 1-3 mm. in diameter, and each spot is seen to con- 
tain a cluster of small, black, rounded elevations, the cluster 



Trees and Timber 



389 



surrounded by a Vjorder of dead tissue. Premature defolia- 
tion results. The disease is prevalent in all parts of the 
United States. 

FILBERT, HAZEL 

Blight "^^^ (Bacteria). — A serious blight, which in many 
respects resembles blight of pear, affects the filbert in Oregon. 
It occurs on buds, shoots, leaves, and 
as cankers on larger limbs. 

Black-knot ^^^ {Cryptosporella anom- 
ala (Peck) Sacc.). — In 1892 Halsted 
noted black-knot as destructive to sev- 
eral hundred trees in New Jersey, and 
in 1893 Humphry described the same 
disease upon hazel canes in Massachu- 
setts. It is characterized by numer- 
ous small, elliptical, warty emergences 
upon the bark of the diseased branches. 
The diseased portions are sunken, 
owing to the contraction of the inner 
bark to a mere line. The girdling pro- 
duced results in death of the affected 
canes and general injury similar to 
that produced by plum knot. Affected 
branches should be cut and burned. 




Fig. 206. — Elm leaf- 
spot. After Heald. 



HEMLOCK, WESTERN {Tsuga heter- 
ophylla) 

Heart-rot ^^^ (Echinodontium tiacto- 
rum E. & E.). — The fungus enters 
through wounds, chiefly branch stubs, and produces a 
stringy brown rot of the heart wood, which extends to all 
parts of the tree. A single sporophore of the fungus on 
the first 16-foot log of the tree trunk may be taken to indicate 
that the heartwood is unmarketable in both the first and 
second logs. The position of the largest sporophore usually 
indicates the region of greatest decay. 



390 Diseases of Economic Plants 

Rust {Melampsorella elatina (A. & S.) Arth, ^cidium). — 
This cluster-cup fungus produces bushy distortions, ''witches' 
brooms," by causing profuse branching of the affected part 
of the tree. These abnormal branches soon lose their leaves, 
and cluster-cups are produced upon them. The brooms are 
perennial and increase in size each year, in some cases largely 
covering a whole tree with the brooms. In such cases the 
trees are stunted and may even be killed. Infection may 
be reduced by destroying the spore-bearing branches or by 
eliminating the alternate hosts, Alsine and Cerastium. 

Canker (Dasyscypha resinaria (C. & P.) Rehm). — Swollen 
cankers occur in the stems and branches, even girdling the 
main trunk and killing the tree. After the branch is dead the 
causal fungus produces spores in small disks, orange-colored 
within, about 4-6 mm. wide and high. 

HORSE-CHESTNUT, BUCKEYE 

Leaf-blotch ^^^ {Guignardia cesculi (Pk.) Stew., Phyllosticta) . 
— Unsightly spots upon the leaflets, and premature defolia- 
tion, render this the most conspicuous disease of this tree. 
The brown spots are at first circular, but as they enlarge 
are limited by the larger ribs, thus becoming nearly rect- 
angular. Pycnidia may be seen by means of a lens. This 
is a decided nursery pest and is also troublesome on park 
plantings. 

Lime-sulfur or Bordeaux mixture have much reduced 
the spotting. Dusting (sulfur, 90 parts, arsenate of lead, 10 
parts) has also proved effective. 

LARCH 

Mistletoe ^^^ (Razoumofskya) . — This is the chief enemy 
of the western larch, attacking trees of all ages. If the trees 
are not killed they produce but a poor grade of timber and 
poor growth, and are moreover rendered liable to the at- 
tacks of wood-rotting fungi. All larches infected with 
mistletoe should be cut, whether salable or not. 



Trees and Timber 



391 



LINDEN 

Leaf-Spot (Cercospora microsora Sacc). — Small, circular 
or large, irregular, dead spots of the leaf indicate the presence 
of this disease. It has been reported as destructive in Mas- 




FiG. 207. — Mistletoe. After U. S. Bur. PL Ind. 

sachusetts, New Jersey, and New York. Two sprayings in 
Massachusetts resulted in longer retention of the foliage and 
lessened infection. 



LOCUST 

Yellow wood-rot ^^"^ {Fomes rimosus Berk.). — From 
Massachusetts to New Mexico, over the entire black locust 
territory, this heart-rot prevails. It is a yellow rot extending 



392 Diseases of Economic Plants 

from the center outward in radial lines through the medullary 
rays; the hard flinty wood is reduced to a soft, yellow, cheesy 
mass, spongy when wet. The pore-bearing, shelving, hoof- 
shaped, sporophores develop chiefly from the burrows of 
the locust borers or from stubs. The young portions are 
light brown; older parts, dark to black and fissured. The 
lower side is dull red-brown. 

The rot ceases with the death of the tree, and posts made 
from diseased wood do not continue to rot. 



MAPLE 

Leaf-Spot (Phyllosticta acericola C. & E.). — A large propor- 
tion of the leaf may become involved, causing premature 
defoliation which materially lessens the value of the tree for 
ornament or shade. The silver maples are especially sus- 
ceptible, and their sale has thereby been reduced. The leaf 
spot was first noted in 1874 and is distributed throughout the 
United States. The blackish, subcircular spots as they en- 
large change to brown and later to dirty white in the center 
with black borders. Small black pycnidia may be seen in the 
central regions of the mature spots, which are from 10-14 mm. 
in diameter. Burning diseased leaves is recommended, ac- 
companied by use of Bordeaux mixture if economy justifies. 

Tar-spot (Rhytisma acerinum Fr.). — Thick, shining, 
irregular black spots 1-1.5 cm. across appear on the leaves in 
late summer and cause them to fall prematurely, thus weak- 
ening the tree. Considerable damage is often done to nur- 
sery stock. The leaves should be raked together and burned 
in the fall. 

Leaf-spot {Rhytisma pundatum Fr.). — In this leaf-spot 
the causal fungus forms several small, black dots upon the 
leaves as contrasted with the one large black blotch of the 
tar-spot. 

Anthracnose (Glceosporium apocryptum E. & E.). — Nur- 
sery maples have been seriously injured by this anthracnose. 
The tips of leaves of pruned twigs turn yellow, then blacken 



Trees and Timber 



393 



and die as though frosted. Young leaves and shoots are 
killed and by their death induce abnormal branching, result- 
ing in a compact head. The disease seems limited to young 
trees. 

Bordeaux mixture is advised — three or more sprayings. 




Fig. 208. — Maple tar-spot. After Heald. 

Thrombosis {V erticillium) . — Leaves wilt and branches 
die due to plugging of the veins by the fungus. Dark streaks 
show in the wood of affected twigs. 



MULBERRY 

Blight {Bacterium mori B. & L.). — Upon the leaf small, 
reddish-brown spots, pellucid when moist, are produced. 



394 Diseases of Economic Plants 

The twigs and even entire trees are stunted and yellowed. 
Cankers may almost or quite girdle the stem, the diseased 
area becoming dark. Prune as for blight of pear. 

OAK 

Leaf-curl ^^^ {Taphrina coerulescens (D. & M.) Tul.). — 
Though close kin to peach curl, only a small proportion of 
each leaf, spots 1-2 cm. in diameter, is involved. Defoliation 
may result in extreme cases, and continued disease each 
year may cause death. Affected leaves should be burned 
and if the tree value warrants it sprayed as for peach curl. 
Powdery-mildews (Microsphcera) . — These appear late and 
do little harm except upon nursery stock. Flowers of sul- 
fur or Bordeaux mixture are useful. Twig-blight {Diplodia 
longispora C. & E.) does some injury. Blight. See sycamore. 

OSAGE ORANGE 

Rust (Physopella fid (Cast.) Arth.). — The sori which 
are scattered thickly over large areas of the lower side of 
the leaf are small, 0.1-0.3 mm. in diameter and are pale 
cinnamon-brown. This rust is known from South Carolina 
to Texas. 



PECAN 



415, 416 



Scab {Fusidadium effusum Wint.). — In the Southern 
States, particularly Florida, Louisiana, Georgia, Oklahoma, 
and Texas, twigs, leaves, and nuts are affected with a dark 
green, smoky, superficial growth. Upon leaves and petioles 
dead spots, distortion, and defoliation are caused. The new 
growth of twig is often killed, but the greatest injury is to the 
nuts which drop before maturity. 

Spraying with lime-sulfur or Bordeaux mixture, or dusting 
with sulfur has proved effective. 

Powdery-mildew (Microsphcera alni (Wallr.) Salm.). — 
During certain years in the South the pecan crop has been 



Trees and Timber 395 

much injured by this mildew. It is recognized as a flour-Uke, 
white coating and is particularly damaging to the young nuts. 

Spraying with Bordeaux mixture or lime-sulfur before the 
fungus appears is effective. Burning of infested fall refuse 
is also helpful. 

Anthracnose (Glomerella cingulata, Gloeosporium) . — Large, 
light brown to reddish blotches occur on the leaves and cause 
them to fall. The nut hulls bear irregular, sunken, black 
blotches which may extend to the whole surface, and which 
eventually bear numerous pink acervuli. Many nuts fall 
prematurely. 

All infested refuse should be burned; a dormant spray ap- 
plied, another spraying given just after the buds open, and 
if need be, one to three additional sprayings later. 

Rosette. "^^^^ ^^^ — From 10 to 20 per cent of the trees in 
the Southeast are affected. The leaves at the branch ends 
are first yellow-mottled, then die. Later the twigs die back 
and the trees are seriously weakened. No parasite is present; 
the disease seems to result from deficiency of humus, food 
material, and moisture, and may largely be avoided by 
use of legumes, and by plowing under green cover crops. 

Die-back {Botryosphceria berengeriana de Not.). — Young 
twigs die and their surfaces bear numerous black perithecia. 
Dead wood should be pruned out and burned. Pink-mold 
{Cephalothecium sp.) affects the hulls, nut, and the embryo. 
It frequently follows scab. Brown leaf-spot (Cercospora fusca 
(H. & W.) Rand.), Nursery-blight (Phyllosticta caryoe Pk.), a 
kernel-spot {Coniothyrium) and Mistletoe do some damage. 
Pollen-blight (Microstroma juglandis (Ber.) Sacc. var. robus- 
tum Hig.) presents an interesting case of a fungus parasitic 
in the anthers. 

PINE 

Blister-rust ^^'^' ^-^ {Cronartium ribicola F. deW., Perider- 
mium) . — This rust which has done much damage in north- 
ern Europe on the 5-leaved or white pines, of which there 
are some eighteen species, entered the United States in 



396 



Diseases of Economic Plants 



quantity from Germany, between 1900 and 1909 on diseased 
pine seedlings, though isolated cases occurred here prior to 
those dates, even as early as 1892. It is now known in 
Maine, New Hampshire, Vermont, Massachusetts, Con- 




FiG. 209. — Map showing general location of pine blister infections. 

^ Diseased white pines found in 1816. 

• Diseased currants and gooseberries found in 1916. 

j^ Areas of heavily infected currants and gooseberries. 
!:X, Centers of heavy infection where the principal efforts were made 
"^ to eradicate diseased plants. 

(Three centers of infection also exist in Wisconsin and Minnesota.) 
Courtesy of the Office of Forest Pathology. 

necticut. New York, Pennsylvania, Rhode Island, New 
Jersey, Kansas, Ohio, Indiana, Wisconsin, Minnesota. The 
alternate host is Ribes (see p. 116), some twenty-one species 
of which are susceptible. In the spring, sporidia from the 



Trees and Timber 397 

Ribes telial stage of the rust may infect pines on which they 
fall. The first external evidence of disease appears one to 
several years later. The bark thickens and later pycnia 
develop. In the spring, secia, numerous or few, mature on the 
swollen bark and free their orange-colored spores. These 
spores falling on Ribes produce the next stage of the rust, 
though they cannot directly infect pine. The rust is peren- 
nial in the pine, the cankers enlarging year after year. Trees 
attacked when 3'oung, c. g., under 25 years of age, are liable 
to be killed. Older trees may merely lose branches or the 
central, top shoot. The damage to white pines is very 
serious. In 1909 the value of standing white pine was esti- 
mated at $600,000,000, the sugar pine at $120,000,000. A 
loss of even 1 per cent of this, which is a low estimate, is 
significant. 

In 1912 laws were enacted to prevent entry into the United 
States of foreign stock likely to harbor and introduce dan- 
gerous fungi and insect pests. Rigid Federal and state 
inspection is now exercised to prevent further spread of this 
disease. Imported Ribes and white pine must be kept well 
separated. If the disease is present, all Ribes should be 
removed from the vicinity. At the present time, $530,448 
of Federal appropriations and $267,300 of state funds have 
been used to combat this disease. 

Bluing ^^^ (Ceratostomella pilifera (Fr.) Wint.). — The 
characteristic symptom, bluing of the sapwood, begins in 
August and September after the trees have been attacked 
by beetles. The blue color starts near the base of the tree 
and gradually spreads upward until the entire sapwood be- 
comes blue. The presence of the mycelium of the above- 
named fungus, which gains entrance through openings made 
by the beetle and is initiated by spores carried by the beetle 
is responsible for the color phenomenon. Blue wood is as 
strong as normal, green wood, is tougher, and when dry, it 
will last as long; but when wet, it rots rapidly. 

Leaf-cast (Hypoderma) . — The needles die from the tips 
toward the bases, becoming first reddish, then gray. Black 



398 



Diseases of Economic Plants 



lines which extend lengthwise of the leaves arfe produced by 
the ascus-bearing organs. 

Premature defoliation results. 




Fig. 210. — Cronartium ribicola on pine showing general aspect of 

disease. After Colley. 

Leaf-blight, twig-blight {Lophodermium hrachysporum 
Rostr.). — In Maine the leaf -blight has been noted as de- 
structive to a considerable number of small trees and in- 



Trees and Timber 



399 



juring the lower branches of large trees; serious damage, 
however, is not common. 

Damping-off {Fusarium sp.). — The general characters 
are those mentioned under damping-off. It is serious in 




Fig. 211. — Cronartium ribicola on pine show- 
ing sporiferous pustules. After Colley. 

Vermont, New York, Missouri, and probably in many other 
states, killing the seedlings in nurseries as soon as they ap- 
pear above ground. The beds should be given all ventilation 
possible. A top-dressing of steriHzed sand sprinkled over the 
beds immediately after germination resulted in 30 per cent 
of disease against 42 per cent in the untreated part. For dis- 
infection of soil, see p. 460. 



400 



Diseases of Economic Plants 



Rust (Cronartium cerebrum (Pk.) H. & L., Peridermium). — 
Swollen areas occur upon the branches and young stems 
which are gradually killed. The gall-like growth sheds a 




Fig. 212. ^ Gall produced by Cronartium (Perider- 
mium) cerebrum on pine. After Hedgcock. 



profusion of orange-colored spores each spring. Chiefly by 
its interference with the sap current the swellings bring about 
the death of many trees. The galls are perennial and may 



Trees and Timber 



401 



persist for many years. One stage of this rust occurs upon 
the oaks. 

Rust (C oleosporium solidaginis (Schw.) Thtim., Perider- 
mium). — Another species of Peridermium occurs upon 
leaves, producing small, sac-like, tubular outgrowths which 

contain the spores. Tliis is a stage of 

a rust which appears later in the season 
upon golden-rods and asters. 

Red-rot {Fomes pinicola Cke.). — 
Upon dead trees this rot begins just 
under the bark, usually near the tree 
top, often following bluing. The wood 
is at first wet and soggy, but soon 
becomes brittle, so that it crumbles 
readily. The cracks become filled with 
felted fungous threads. The sporo- 
phores first appear as fleshy knots, 
soon red, which widen to pore-bearing 
shelves. 



POPLAR, COTTONWOOD 

Rust {Melampsora sps.). — This is 
similar to willow rust. See p. 405. 

European-canker ^-- (Dothichiza pop- 
ulea S. & B.). — Species of poplar and 
Cottonwood in nine states show this 
disease. Death of the cambium re- 
sults, and following this numerous can- 
kers and dead branches render the trees 
unsightly. The disease was probably 
recently imported on the Lombardy 
poplar from Europe. New stock should 
be carefully inspected. Infected wood 
should be cut out and burned. 

Canker '^^^ {Cytospora chrysosperma (Pers.) Fr.). — This 
serious canker is prevalent in the southwestern United States 




Fig. 213. — Pine 
needle, bearing clus- 
ter-cup of rust, en- 
larged. After Clin- 
ton. 



402 Diseases of Economic Plants 

on willow and poplar, the lesions occurring on the trunks, 
limbs, and twigs, with reddish pycnidia on the dead areas 
near the edge of the canker or over the entire dead surface. 
Strict inspection should guard against further spread of 
the disease. Resistant varieties should be used, the trees 
given plenty of water and protected against mechanical 
injury. 

Leaf -blight (Marssonina populi (Lib.) Sacc). — Primary 
infection occurs upon the leaves, resulting in small, 3-8 min., 
circular, black dead spots which are quite definitely bordered. 
As the leaves die, the patches upon the stems also turn black 
and die. Infection proceeds to the supporting twigs and may 
result in dead patches of bark upon quite large shoots. 

Cutting and burning infected twigs is advised. 

Galls {Macrophoma tumefaciens Sh.) occur on the branches. 



RUBBER 



158 



Trees and shrubs that produce rubber are subject to 
numerous destructive diseases, among them Cankers due to 
various species of Nectria, Corticium, Fusicladium, and Di- 
plodia; Die-back (Thyridaria) which kills the young shoots; 
seedling diseases due to Pestalozzia, Helminthosporium and 
numerous leaf fungi, and Root-rot due to Fomes, Irpex, 
Hymenochaete and Poria. 

SASSAFRAS 

Heart-rot {Fames rihis (Sch.) Fr.). — Spaulding in 1907 
described this rot as a serious injury to sassafras in Missouri. 
It is also found upon stems and roots of various shrubby 
plants, as rose and currant. By means of a wound the attack 
is made upon exposed heart wood, proceeding slowly into the 
sap wood. The sassafras is thus immune until it reaches an 
age bearing heart wood. The decaying wood is abnormally 
light in color and slightly reddish, and the affected region is 
bounded by a narrow black zone. Trees sometimes die from 
the attack. 



Trees and Timber 



403 



The causal fungus has been reported in America from 
Kansas, Missouri, New York, and New Jersey. 



SYCAMORE 

Blight (Gnomonia veneta (S. & S.) Kleb.. Gloeosporium) . — 
First noted in 1848, this anthracnose is very widely dis- 
tributed on sycamore and oak 
from New Jersey to California 
and Mississippi. In extreme 
cases it may so weaken the trees 
as to cause their death. The 
scorched appearance of the 
leaves and defoliation render 
the trees unsightly. Just before 
they become full-grown the 
leaves give the first indication 
of the attack. Beginning near 
the veins or ribs or upon the 
petiole, the disease causes a 
stoppage of the water supply 
to the more distant portions of 
the leaf, resulting in dead areas. 

Dead twigs should be pruned 
out, and infected material col- 
lected and burned. Spraying 
with Bordeaux mixture may be 
practiced if the expense is war- 
ranted. 

WALNUT 

Anthracnose {Gnomonia lepto- 
styla (Fries) C. & d. Not. Mars- 
sonina) . — Conspicuous brown 

spots, 2-4 mm. in diameter, -r. oi^ w i ^ ^ • 

^ ' ii 1 n 1-1 Fig. 214. — Walnut twig 

appear upon the leaflets, which blighted by bacteria. After 

soon yellow and fall. Upon the R. E. Smith. 




404 Diseases of Economic Plants 

lower sides of the leaf spots are small, concentrically ar- 
ranged, black acervuli. 

The disease has been troublesome on black-walnut in 
Delaware, Iowa, Maryland, and West Virginia. 

Blight '^"^' '^^'* {Pseudomonas juglandis Pierce). — This 
blight known in 1901 only on the Pacific coast is now recorded 
in California, Oregon, Texas, Louisiana, Maryland, Delaware, 
Pennsylvania, and New York on English-walnut. 

Black cankered spots upon the young nuts, which fall pre- 
maturely, or similar spots upon the young, green shoots are 
characteristic. Chief damage is to the nuts, but in seasons. 




Fig. 215. — Bacterial blight of walnuts. After R. E. Smith. 

favorable to blight much of the terminal growth is killed and 
the succeeding crop is thereby reduced. 

Spraying is of questionable value. Care should be taken 
to select resistant trees for propagation. 

Melaxuma ^-^ (Dothiorella gregaria Sacc). — In this dis- 
ease, reported from California, black sunken cankers develop 
on the trunk and larger limbs, and the leaves on the smaller 
limbs suddenly wilt. The first indication of disease is often a 
black area like a blotch of tar on the gray bark. Excision and 
disinfection should be practiced. 

Other walnut troubles are : Die-back, often due to lack of or 



Trees and Timber 405 

excess of soil moisture; Sun-burn of nuts or tree trunk; 
Crown-gall; Perforation, an imperfection in shell develop- 
ment; Root-rot; Wilt ; Yellows ; and Leaf-spot (Marssonina). 

WILLOW 

Rust {Melampsora saliciscaprce (Pers.) Wint.). — Of tree 
rusts this is one of the most prevalent, occurring as dusty, 
yellow sori upon the lower leaf surfaces. Trees are rendered 
unsightly by the defoliation induced. In the latter part of 
the season the winter sori appear as reddish brown to black, 
waxy or crusty spots. A similar rust is common upon cotton- 
wood, Balm of Gilead, poplar. Canker (Cytospora). — See 
poplar. 



ORNAMENTAL PLANTS 

The ornamentals give rise to problems unique in the field 
of plant pathology due to the fact that the number of species 
of plants involved is much larger than with any other group 
of crop plants, and moreover, because they vary greatly in 
value; some of them, as for example the rare orchids, have a 
market value higher than that of any other individual culti- 
vated plant; other ornamentals are of negligible commercial 
value. There is large diversity of financial interest; some 
crops are grown on a large scale by only a few individuals, 
others to considerable extent by nurserymen and seedmen, 
other crops are rarities in only a few greenhouses, while to 
many the flower garden in the yard has a high sentimental, 
though small money, value. Aside from a few standard 
flowers, as for example roses, violets, chrysanthemums, 
carnations, etc., and certain nursery stock, so few individuals 
are interested, or have so small a financial risk in these crops 
that large expenditures of public funds have not been made 
for investigation or control of the diseases. The result is 
that aside from the standard ornamental crops and a few 
isolated cases of other crops, the diseases have received no 
such complete study as has been given for example to diseases 
of other plants of general interest and large commercial 
value. Indeed in many cases knowledge is limited to a mere 
note of the occurrence of certain diseases or parasites, and the 
course of procedure is only to be inferred from knowledge of 
similar diseases. Flower fanciers and the commercial growers 
of ornamentals are able and willing and can well afford to use 
the best methods of treatment, and it is unfortunate that so 
much is lacking here concerning treatment for the specific 
diseases. * 

406 



Ornamental Plants 407 

General Diseases 

Powdery-mildews. — For description, see p. 122. 

These diseases are particularly common on ornamentals un- 
der glass or in the open. The following Hst comprises the hosts 
on which they are most frequently found; Adonis, Alyssum, 
Anemone, Aquilegia, Begonia, Berberis, Calendula, Chrysan- 
themum, p. 420, Clematis, Coreopsis, Cosmos, Dahlia, p. 421, 
golden glow, hawthorn, honeysuckle, lilac, p. 426, larkspur, 
peony, phlox, p. 429, rose, p. 431, spirea, sunflower, sweet pea, 
p. 435, verbena, p. 436, violet, Virginian creeper. 

In-door or out-of-door treatments are essentially those 
given under rose mildew (p. 432). 

Cutting-bench and Seed-bed Diseases. — If plants in the 
cutting-bench are wounded or weak they are subject to attack 
by many fungi that could not injure them under normal con- 
ditions. The chief point in preventing inroads by these fungi 
is to keep the cutting-bench and seed bed in good sanitary 
condition, i. e., proper degree of moisture and temperature, 
well ventilated, and free from infestation by injurious fungi. 
Soil and bench, if once infested, should be disinfected (p. 460). 
No diseased refuse should be allowed to contaminate it. The 
chief trouble in the seed bed is damping-off (p. 19). 

Stem-rot iCoriicium). — See p. 21. Numerous plants 
are affected, among them: Abutilon, Acalypha, Achillea, 
Ageratum, Alyssum, Amarantus, Antirrhinum, Aquilegia, 
Asparagus, Aucuba, Bartonia, Begonia, Berberis, Calendula, 
Callistephus, Campanula, Celosia, Centaurea, Chrysanthe- 
mum, Cineraria, Coleus, Coreopsis, Cuphea, Dianthus, 
Eriobotrya, Erysimum, Euphorbia, Godetia, Gypsophila, 
Helianthus, Hibiscus, Iberis, Impatiens, Iresine, Kochia, 
Lathyrus, Lavatera, Ligustrum, Linaria, Linum, Lobelia, 
Lychnis, Lythrum, Matthiola, Paeonia, Pelargonium, Petu- 
nia, Phlox, Physalis, Piqueria, Platycodon, Portulaca, 
Potentilla, Primula, Punica, Pyrethrum, Reseda, Richardia, 
Ricinus, Salvia, Santolina, Schizanthus, Sedum, Seradella, 
Silene, Stachys, Taxus, Telanthera, Verbena, Vinca, Viola. 



408 Diseases of Economic Plants 

Slime-mold (Physarum cinereum (Bat.) Pers.). — This 
mold grows as a slimy mass over any plants that are in its 
path, often covering an area a meter square. It later changes 
to the gray, dusty, sporing stage. It is not really parasitic or 
even injurious, but by its unsightliness, arouses the apprehen- 
sion of the gardener. No treatment is needed. 

"Root-TOt (Thielavia). See p. 23. Among the ornamentals, 
this disease has been noted particularly on Aralia, Begonia, 
Cyclamen, Dahlia, sweet pea, violet, Tropoeolum. 

Sooty-mold (Capnodium) may occur on almost any plant, 
though usually with little or no injury. It is most harmful 
on the camelha. (See p. 413). Other plants on which it is 
often seen are privet, Lonicera, palms, Cornus, yew, oleander, 
rhododendron. 

Crown-gall (Pseudomonas) . See p. 87. Crown-gall is not 
usually troublesome on ornamentals. It has been noted on 
daisy. Evonymus, honeysuckle, rose, flowering almond, 
chrysanthemum . 

Southern-blight {Sclerotium rolfsii). See p. 23. The fun- 
gus that causes this disease may be found on almost any 
host, especially in the South. Even as far north as Illinois 
it was destructive in gardens on Campanula, Erigeron, 
Dianthus, Dracocephalum, Pentstemon, Phlox, Eupatorium. 



Special Diseases 
AGAVE 

Anthracnose (Colletotrichum agaves Cav.). — Spots are 
produced on the leaves, and often cause the death of young 
plants. Diseased leaves should be removed and burned, and 
the remaining leaves sprayed. 

AMARANTUS (Various cultivated varieties). 

White-rust (Albugo) is common but not serious. See 
p. 164. 



Ornamental Plants 409 

ANDROMEDA 

Gall {Exobasidium sps.). — See azalea. 

ANEMONE 

Rust (Cluster-cup) . — The alternate stage of the rust of 
drupes occurs here. Drop (Sclerotinia tuberosa Fcl.) also 
occurs occasionally. 

ASPIDISTRA 

Anthracnose (Colletotrichum omnivorum Hals.) is common 
everywhere especially upon variegated plants. 

ASTER, CHINA (Callistephus) 

Wilt ^^^' ^^"^ {Fusarium conglutinans Wall. var. callistephani' 
Beach.). — The wilt, mentioned as early as 1896 by Gallo- 
way, has since been reported from Massachusetts and Colo- 
rado, and is probably the most important disease of the 
China aster. The time of transplanting the beds and blossom- 
ing time are most susceptible periods, though the wilt is 
present to some extent at other times. 

The most conspicuous symptom is the sudden death of 
the plants. The bark of the stem is rotted at the ground line. 
Close observation earlier shows the leaves upon one side of 
the plant, particularly the lower leaves, yellowed and wilted, 
and the youngest leaves to be smaller than normal. The wilt- 
ing effect may sometimes be found first on one side only of 
one of the lower leaves. Plants attacked early may die, or 
in milder cases may survive to produce a few small blooms. 
If the symptoms first show at blooming time, their sequence 
is the same. 

The roots in early stages appear healthy, but the stem 
near the ground, in longitudinal section, shows darkening 
of the outer wood, local at first upon the affected side, but 
extending rapidly in all directions. Eventually the dis- 
coloration extends into the bark, which rots away. 



410 



Diseases of Economic Plants 



In the seed bed the same disease may occur as damping- 
off. See p. 19. It seems that original infection always oc- 
curs in the seed bed, never in the open. 

Plants started in the open are not susceptible. If it is 
necessary to start them under glass, too thick sowing should 
be avoided, and they should be ventilated thoroughly. 

Soil that is known to be in- 
fested should not be used. 
The disease may be pre- 
vented by avoidance of the 
conditions that favor damp- 
ing-off. 

Yellows. ^-^ — Growth is 
spindling and the shoots and 
leaves are yellow, but no 
death of affected parts 
occurs. In badly diseased 
plants no flowers, or only 
rudiments of such, develop 
upon the sick shoots. In 
other cases the flowers turn 
greenish-yellow, wholly or 
in part, with malformed 
floral parts producing little 
or no seed. No parasites 
are present and the cause 
of the condition is unknown, 
but the striking similarity 
to peach yellows is obvious. 
The same disease affects the marguerite. 

Rust {Coleosporium solidaginis (Schw.) Thuem.). — 
Orange-red sori, waxy in consistency, are produced in great 
numbers upon the leaves, which when badly affected curl, 
die, and thus bring about the death of the plant. Stem- 
rot {Corticium). — See p. 21. 




Fig. 216. — Rust on barberry. 
After Stakman. 



Ornamental Plants 



411 



AZALEA 

Leaf-spot (Septoria) is common on the leaves. Gall 
{Exohasidium sps.). — Leaves, flowers, or shoots are en- 
larged and distorted. Diseased parts should be cut and 
burned and the plant sprayed with Bordeaux mixture. 



BALM, SILVER 

Rust (Puccinia men- 
thce Pers.). — Some 
thirty species of the 
mint family, including 
peppermint, thyme, 
catnip, monarda, are 
affected by this rust. 
It is recognized by 
its sori, which are at 
first cinnamon-colored, 
later chestnut-brown. 
Badly diseased leaves 
curl and die. 

Infested refuse 
should be burned. 

BAMBOO 

Smut ( Usttlago shir- 
aiana Hem.). — The 
short branches still 
covered by the leaf 
sheaths are attacked. 



f 





%>- 




Tig. 217. — Barberry rust enlarged. 
After Stakman. 



Witches-brooms are frequently formed. It has been found 
in this country on two species of bamboo. Diseased plants 
should be burned. 

BARBERRY 

Rust (Puccinia graminis, .^cidium). — This is of chief 
interest on account of the damage the other stages of the 



412 Diseases of Economic Plants 

rust causes to cereals. Rusts from many grasses pass to 
the common barberry though not to the Japanese bar- 
berry. See p. 277. 

Wilt {Verticillium alboatrum R. & B.) affects the Japanese 
barberry. The fohage turns yellow or red; the sapwood is 
streaked with dark lines; ultimately the wood turns black. 
Frequently the disease is severe. 

BEGONIA 

Eel-worms in the leaves cause translucent watery spots. 
Powdery-mildew does some harm. 

BLETIA 

Anthracnose (Colletotrichum hletice Hals.). — The leaves 
of this orchid are frequently disfigured by very dark, almost 
black spots. In late stages the dead tissue falls away, leaving 
merely shreds of veins traversing the place of disease. 

The tips of the leaves are often frayed. 

Volutella rot (Volutella concentrica Hals.). — Numerous 
lemon-colored acervuli surrounded by concentric bluish 
rings render these spots different from those above described. 

CALLA 

Soft-rot ''-^ (Bacillus carotovorus Jones). — A large annual 
loss and frequently the abandonment of calla growing is due 
to this disease, which is known throughout the United States. 

The affected plants rot off near the soil surface, and the 
rot progresses from this point up into the leaves or down 
into the corm. Usually the rot first shows at the top of the 
corm, but in some instances it is seen first at the edge of a 
petiole, or on the corm below ground. 

In section the diseased portion is brown, soft, and watery. 
Leaves whose bases are diseased become pale at the edges, 
then brown. Similar changes occur in spots on the leaf, and 
the whole leaf eventually dies, or the rot may progress so 
rapidly that the leaf falls before losing its green color. The 



Ornamental Plants 413 

flower or its stalk are similarly diseased. Through the corm 
the roots are reached. Here the skin is unaffected and re- 
mains as a parchment-like tube filled with the creamy residue 
of decay. Rot of the bulb may be arrested by unfavorable 
conditions and show only as dark sunken spots. 

The course of the disease extends from a few days to several 
weeks, or the disease may lie dormant for months, even 
from season to season. Such cases of dormant disease carry 
the infestation to the succeeding crop and in commercial 
corms from country to country. The rot spreads rapidly 
from plant to plant by way of the diseased roots and through 
the soil itself. The causal bacillus remains in the soil and may 
attack healthy corms planted therein at later periods. 

No known treatment of diseased plants is practicable. 
Infestation of soil may be prevented by careful inspection 
of all corms so as to avoid diseased ones. It is best to test 
commercial corms in pots to be assured of their healthful- 
ness before putting them in the beds. All soil from badly 
infested beds should be disinfected or removed and fresh 
soil supplied. 

Leaf-spot {Phyllosficta richardiw Hals.). — Blighted leaves 
bear large ashen spots upon which are numerous minute dark 
pycnidia. 

Another Leaf-spot due to Cercospora richardicecola Atk. 
was first mentioned by Atkinson in 1891 as occurring in Ala- 
bama. The edges of the leaves turn black in circular spots. 

CAMELLIA 

Sooty-mold {Capnodium sp.). — The sooty -mold is perhaps 
more injurious on this plant than on any other ornamental, 
not as an actual disease but by injury to salability of the foli- 
age. Leaf-spot {Pestalozzia guepini Desm.) is common. 

CANNA 

Rust {Puccinia cannce (Wint.) P. Henn.). — This true rust 
is common and injurious in the warmer climates but is rare 
in the more temperate regions. 



414 Diseases of Economic Plants 

CARNATION 

Rust ^"^' "^^^ {Urornyces caryophyllinus (Sch.) Wint.). — 
The carnation rust was first described in 1789 in Germany 
and was noted in the United States by Arthur in 1891, 
evidently a recent importation. It rapidly became wide- 
spread through sale of infected plants and cuttings and was 
soon present in almost all greenhouses. Though widely 
known in Europe, it did not seem to be especially destructive 
there; but upon entrance into America its character changed 
to that of an aggressive pest, and ruin was brought to the 
beds in many greenhouses. The entire contents of large 
houses valued at thousands of dollars was in many instances 
utterly lost. After a short period of extreme destructiveness, 
which was at its height about 1893, the vigor of the attack 
waned, until to-day the pest does only a small fraction of 
damage as compared with that of the early years of its inva- 
sion, though it still causes one of the serious carnation 
diseases. 

The rust is easily recognized by the sori filled with powdery, 
brown spores. The sori, at first covered by the white epider- 
mis, are 1-2 mm. in diameter, round or elongated in the 
direction of the length of the stem or leaf. When very 
numerous, the affected part is slightly bleached or yellowed 
and appears swollen, owing to the much-ruptured epidermis. 
The mycelium of the causal fungus is usually general through- 
out affected plants, but may, in case of new infection, be 
limited to the immediate region of the sorus. 

There is much difference in varietal resistance, a fact that 
should receive due weight in the selection of varieties for 
culture. 

Cuttings should never be taken from diseased stock. 
If there is doubt as to the presence of superficial spores, it is 
well to dip the cuttings in potassium sulfid, one ounce 
to one gallon. A weekly protective spray of copper sul- 
fate, one pound to twenty-five gallons, throughout the life 
of the plant is also recommended. The leaves should be 



Ornamental Plants 415 

kept as free from moisture as possible by free ventilation, 
and still better by subirrigation. 

Fumigation of the houses in the fall before the intro- 
duction of the plants serves to lessen infection from old 
spores. 

Rust sori are occasionally the seat of attack b}^ a Fu- 
sarium,^^^ the result being a leaf-spot a centimeter or more 
in diameter. 

Leaf-spot {Septoria dianthi Desm.). — The spots of this 
disease — usualh^ upon the leaves, sometimes upon the 
stems — are circular or oblong, blanched or pinkish, and 
purple bordered. Numerous small, black pycnidia lie in 
the central region. The disease is especially abundant upon 
the lower portion of the leaves and the sheaths. The diseased 
part often becomes contracted, which results in bending and 
curling of the leaves. Surface watering of the plants or 
humid atmosphere tend to increase the trouble. 

Another Leaf-spot is due to Vermicularia subeffigurata 
Schw. — The bases of the leaves or the stems are usually the 
points of attack. Black spore-bearing bodies appear in 
abundance. Spraying with ammoniacal copper carbonate 
has given good results. 

Altemariose "'^^ (Alternaria dianthi S. & H.). — This leaf 
and stem disease has been reported as quite troublesome 
in Connecticut, Pennsylvania, District of Columbia, North 
Carolina, Missouri, and elsewhere. It consists of spots 
mostly upon the leaves, sometimes upon the stems, especially 
at the nodes. These are strikingly characteristic, of ashen 
whiteness, with the centers occupied by a scanty, to profuse, 
black fungous growth. The diseased spot is dry, somewhat 
shrunken, thinner than healthy portions of the leaf, approx- 
imately circular, though often somewhat elongated in the 
direction of the longitudinal axis of the leaf. When at 
the node, the disease usually involves the bases of both of 
the leaves, as well as the stem between them. As these 
nodal spots age, the disease penetrates through the stem, 
killing its tissue, which shrinks somewhat and becomes soft 



416 Diseases of Economic Plants 

and disintegrated, resulting in the death of the more distal 
portions of the plant. 

A striking feature is the tendency of this disease to infect 
to a large degree one variety, the Mrs. Thomas W. Lawson, 
to the exemption of others. 

Stem-rot, wilt ^^" {Fusarium sp.). — Described in 1897 by 
Sturgis, this rot occurs chiefly upon the stems and larger 
branches, discoloring the wood and killing the bark, but 
rarely causing soft rot. The diseased plant dies gradually 
with yellowing and drying of the foliage, much as though 
due to insufficient water supply. 

When practicable, beds should be disinfected, and new 
uninfected stock introduced. The disease when first intro- 
duced upon a few plants can be stopped by the immediate 
removal and destruction by fire of the diseased plants. 

Leaf-mold. {Heterosporium echinulatum (Berk.) Cke.). — 
Circular spots, 1-4 mm. in diameter, bearing more or less 
concentric zones of dark mold, appear upon the leaves, espe- 
cially the younger ones, also upon the stems and sometimes 
upon the calyx. Mold upon the calyx results in deformed 
flower parts. In some instances the whole top of a plant 
becomes moldy. 

Infested refuse and leaves should be burned and Bordeaux 
mixture employed as a spray. 

Bacterial-spot ^^^' ^^^ (Pseudomonas woodsii (EFS)). — • 
The spots of the leaves and stems are small, usually sur- 
rounded by a narrow water-soaked area, while the center is 
commonly slightly brown. As the spots grow larger they 
resemble Septoria spots with the exception of the water- 
soaked margin. Later they dry and collapse. Badly diseased 
leaves wither. In some cases nearly all the leaves on many 
of the stems are so badly diseased as to be hopeless. 

This trouble can be checked by removing and burning 
all diseased leaves, then spraying with formalin, 1 part to 500. 
A somewhat similar spot caused by Aphides is known as 
Stigmonose. 

Gray-mold {Botrytis sp.). — A gray-mold similar to that 



Ornamental Plants 417 

upon lettuce sometimes attacks the carnation bud, rotting 
it before it opens. 

Infested refuse should be burned and thorough ventilation 
provided. 

Bud-rot ^^'^ {Sporotrichum aiithophilurri Peck). — In this 
malady some buds never open, others fail to expand to 
perfect flowers, still others deviate only slightly from the 
normal. Badly affected flowers, if not picked, wither and 
turn brown — first the petals, then the sepals. All parts of 
the flower within the calyx are eventually affected with a 
rot, and in some cases, though not always, hyphse of the 
causal fungus may be seen with the naked eye. Mites 
are usually present, but they are not responsible for the 
disease. 

Neglect is among the prominent predisposing causes, 
especially the presence of too much water in the soil or air, 
and the accumulation of debris, leaves, trimmings, and other 
organic matter on the benches. 

The disease may cause considerable damage; thus a daily 
loss of from $1.50 to $2 is recorded in one small house. Since 
the buds only are affected, not the plants themselves, no 
permanent injury is done, and clean culture, destruction of 
all refuse which might harbor the fungus, maintenance of 
moisture at the minimum, and the picking and burning of all 
infected buds will soon bring relief. 

Rot (Volutella dianthi Atk.). — The affected parts are 
pale and studded with minute, black acervuli. This disease 
is of greatest injury in the cutting bench. 

Stem-rot ^-^ (Corticium vagum) . — Plants suddenly wilt, 
dry, and die, while the outer portion of the stem becomes soft 
and rotten. Sclerotia as described in connection with potato 
stem-rot are present. For further discussion of stem-rot, 
see p. 21. High growing temperatures and excess of mois- 
ture should be avoided. Infested soil can be disinfected by 
steam. 

Yellows. — Irregular, sunken spots occur. The cause is 
unknown. 



418 Diseases of Economic Plants 

CHRYSANTHEMUM 

Leaf -spot ^^'^ {Septoria chrysanthernella Cav.). — Large 
brown to black blotches, often irregularly circular and of 
indefinite border, appear upon the leaves. These enlarge and 
coalesce to involve the whole leaf, which withers, dies, and 
falls away. 

The lower leaves are first affected, but in later stages all 
the leaves of the plant may be badly spotted, and practically 
complete defoliation may result. Cuttings from infected 
stock should be avoided. All diseased foliage should be 
picked, collected, and burned, and the remaining foliage 
should be sprayed with Bordeaux mixture with addition of 
soap sufficient to form a suds to increase its adhesive power. 
Five or six sprayings during the season are usually sufficient. 
Leaf-spot (Phyllostida chrysanthemi E. & D.). — This 

disease, first described in 1893, 
is very similar to the above, ex- 
cept that the spots are more 
regularly circular, are purplish 
brown, and have a distinct 
border. Pycnidia which may 
often be seen with the naked eye 
are present. 

Wilt (Fusarium sp.) occurs 
occasionally. 

Rust ^^^ {Puccinia chrysan- 
themi Roze) . — Apparently a na- 
tive of Japan, the rust was 
introduced into England (1895) 
and Europe through commercial 

agencies, and similarly into the 
Fig. 218. - Chrysanthemum jj^^^^^ ^^^^ ^^^^^^ -^ ^^^ gj.g^ 
leaf showmg rust son. Ong- ^^^^^ .^ ^^^^ .^ Massachusetts. 

It was rapidly spread throughout 
this country by diseased stock, and is now known in nearly 
all localities where the chrysanthemum is cultivated. The 




Ornamental Plants 



419 



loss occasioned by the diminution in vigor of the plant and 
consequent imperfection of bloom is large. 

The sori, 2-3 mm. in diameter, which are diagnostic, first 
appear as small blisters covered by the epidermis. The 
rupture of this covering dis- 
closes a dark brown mass of 
spores. The sori are usually 
numerous upon the lower leaf 
surface, and the spores form 
dusty coatings upon the 
leaves. Badly affected leaves 
curl; shrivel, and die. The 
plants are dwarfed and fail to 
produce flowers of value. 

All new stock introduced 
to the houses should be care- 
fully inspected and all dis- 
eased stock destroyed by fire. 
New stock should be isolated 
and watched for a month or 
more to be sure that no 
rust develops. If disease ap- 
pears, all affected leaves 
should be picked and burned 
with precautions to avoid 
scattering the spores. If the 
rust continues to appear, all 
parts above ground must be 
destroyed by fire at the end 
of the season, and plants for 
the next year raised in un- 
contaminated soil and house. 

Ray-blight"*^'' {Ascochyta chrysanthemi Stev.). — In this 
disease, described by Stevens as doing considerable damage 
in North Carolina, the ray flowers are blighted, resulting in 
imperfect opening of the buds. Thorough spraying with 
Bordeaux mixture from the beginning of the season until 




Fig. 219. — Chrysanthemum 
blossom distorted with ray- 
blight. Original. 



420 Diseases of Economic Plants 

blossoming, accompanied by destruction of infested refuse, 
has proved a satisfactory treatment. 

Powdery-Tnildev/ {Erysiphe cichoracearum DC, Oidium). — 
This mildew occurs as white, flour-like spots upon the green 
parts of the plant. It is not often serious, but if it should 
become so, can readily be controlled by the means suggested 
for rose mildew. 

Leaf-spot (Cylindrosporium chrysanthemi E. & D.).^ — 
First described in 1893, this closely resembles Septoria spot, 
though it develops somewhat more rapidly and is conse- 
quently more injurious. Often the leaves die and flowers 
fail to form. Treatment is the same as for Septoria leaf- 
spot. 

Gall (Pseudomonas tumefaciens) . — Galls upon the stems 
of this plant have been proved by Smith and Townsend to be 
due to Pseudomonas. Treatment has not yet been discussed. 

CINERARIA 

Rust {Coleosporium senecionis (Schum.) Fr.) is occa- 
sionally serious. 

CLEMATIS 

Stem-rot ''^^' '^'^^ {Ascochyta clematidina (Thuem.) Gloy.). — 
Plants affected with this disease were first noted in 1883. A 
leaf spot is produced; the petioles are affected and the fungus 
grows down to, and girdles the stem at the node. Diseased 
leaves should be removed and the plant sprayed. Leaf-spot 
(Cylindrosporium clematidis E. & E.). — This occurs on 
clematis in propagating houses causing the loss of the lower 
leaves. 

COLOCASIA 

Rot/^^ — Several kinds of rot occur on the cormels, 
prominent among these are the Java black-rot (Diplodia sps.), 
Powdery gray-rot (Fusariuni) , Southern blight (Sclerotium 
rolfsii) ,"*Sof t-rot (Bacillus carotovorus) . 



Ornamental Plants 421 



COSMOS 



Stem-blight ^^^ {Phomopsis stewartii Pk.). — The first 
indication of disease is seen in brown discoloration of the 
stem or branches, the attack often, though not always, 
occurring at a wound. The diseased branches at the point of 
attack are weak and frequently break off. Minute pycnidia 
are present in the diseased parts. The disease appears only 
on mature plants and is very destructive. 

CYCLAMEN 

Leaf-spot {Phoma cydamenw Hal.). — A disease of the 
foliage which sometimes causes almost entire loss of the 
crop is marked by large, dark, irregularly shaped spots 
upon the leaf. These spots later dry, turn lighter in color, 
and show a series of concentric light and dark bands, at the 
same time becoming brittle and often breaking away. Dis- 
eased leaves should be burned and the plants sprayed with 
Bordeaux mixture or ammoniacal copper carbonate. Several 
fungi as Ascochyta, Botrytis, Phyllosticta, Ramularia, Sep- 
toria, cause leaf-spots. 

Anthracnose {Glomerella cingulata var. cyclaminis P. & 
C). — The spots on the leaves are circular, watery, with 
definite borders. Black, hairy acervuli are often present in 
great numbers. 

Nematodes and Thielavia occur on the roots. 

DAHLIA 

Powdery-mildew (Erysiphe communis Wallr, Oidium). — 
This powdery-mildew is quite common, affecting particularly 
the lower leaves late in the season. 

Blight {Phoma dahlice Berk.). — The stems of the flowers 
are the chief seats of attack. The flowers are small and are 
often dropped before opening. Root-rot (Botrytis) occurs in 
storage as a wet soft rot. Wilt (Verticilliutn dahlioe Kleb.). — 
Cf. p. 180. 



422 Diseases of Economic Plants 

DAISY 

Crown-gall (Pseudomonas) does but slight injury. 

DRACAENA 

Leaf-Spot (Phyllosticta niaculicola Hal.). — This may be 
recognized as small, brown, somewhat angular spots on the 
leaves, each spot surrounded by a rather wide yellow border. 
Minute pycnidia are present. 

FERNS 

Blight (Phyllosticta pteridis Hal.). — The tender growing 
tips of ferns are subject to blight, and blighted spots may also 
occur lower upon the leaf. The brown dead tips and leaf 
spots bear minute pycnidia. Blighted parts should be cut 
away and burned and the remaining foliage sprayed with 
Bordeaux mixture. The disease is strictly local, and close 
attention will stop its spread, even after it has considerable 
foothold. Numerous other fungi are recorded on various 
species of ferns, chiefly causing leaf-spots. 

Prothallium-blight (Completoria complens Lohde) . — Upon 
sporelings (prothallia of Aspidium and Pteris) this disease is 
first shown by a yellow or yellow-brown color, as seen in 
mass. Under a hand lens the abnormal color is seen as spots, 
varying from green to yellowish-brown and later to black. 
In later stages disintegration of the affected cells gives the 
prothallia a ragged appearance. 

GERANIUM (Pelargonium) 

Gray-mold (Botrytis sp.). — Frequently this mold appears 
on old blossoms, thence spreads to buds and even to leaves. 
Proper sanitation, destruction of all refuse, and attention to 
ventilation usually prevents this mold. 

Bacterial leaf-spot (Pseudomonas erodii Lew.). — The 
spots are watery, brown when old. The affected leaves fall. 



Ornamental Plants 423 



GLADIOLUS 



Hard-rot ^''^ {Septoria gladioli Pass.). — Leaves are af- 
fected with brown or purplish, irregularly circular spots 
having gray centers and bearing numerous, black pycnidia. 
On the corms lesions appear as water-soaked, dark spots 
which later become sunken and black. The diseased tissue is 
extremely hard. Spraying of seedlings is effective, but a 
simpler method is to plant the seed in soil that has not borne 
Gladioli, and to bring to it no infective material. 

HAWTHORN 

Rust {Gymnosporangium sps.). — The rust, similar to that 
of the apple, is often abundant. 

HEPATICA 

Rust (Transchelia, ^cidium). — This is perennial in the 
plants which should therefore be burned when the rust ap- 
pears. See p. 96. 

HIBISCUS, ROSE-OF-SHARON 

Canker {Cytospora) . — Death of twigs or of whole plants 
results. Diseased parts are thickly covered with wart-like, 
black pycnidia. 

HOLLYHOCK 

Rust (Puccinia malvacearum Mont.). — This rust, native 
to Chili, was introduced into France about 1868. It spread 
rapidly over all Europe, from whence it came to the United 
States about 1886 upon infected seed. It was rapidly dis- 
seminated throughout this country, and is now known from 
Maine to Louisiana, in many places rendering the plants un- 
sightly. It is easily recognized by its yellow to brown sori, 
each sorus considerably raised above the surface of the leaf 



424 Diseases of Economic Plants 

or stein as a small, wart-like protuberance. Badly rusted 
leaves, or even whole plants, wither and die as though 
blighted. In mild cases the leaves remain green and the 
plant may bloom. 

It is recommended to sponge the diseased parts with 
permanganate of potash: two tablespoonfuls of saturated 
solution diluted with one quart of water. 

Leaf-spot {Cercospora althicena S^Ccc). — Upon the leaves 
and other green parts of the hollyhock, velvet leaf, and mal- 
low rather large, dark, angular spots are produced in abund- 
ance, each spot with a dark border and an ashen center upon 
which numerous, black hyphse may be seen. Badly diseased 
leaves fall, and by midsummer only dead, leafless stalks may 
remain. Even in mild cases, by decreasing the amount of 
green surface, the spots both injure the appearance of the 
plant and lessen productiveness. 

Spraying with Bordeaux mixture or ammoniacal copper 
carbonate at intervals of about ten days is thoroughly 
effective. 

Leaf-spot {Phyllosticta althceina Sacc). — This pest, long 
known in Europe, is recognized as large, brown, circular 
spots, 1-2 cm. or more in diameter, upon the leaves. The 
centers are brittle and usually break away irregularly. 

Anthracnose (Colletotrichum malvarum (B. & C.) South.). 
— Since about 1885, this disease has been noticed in destruc- 
tive form in greenhouses, particularly in the propagating 
beds; in some cases to such serious extent as to nearly pro- 
hibit commercial culture of the hollyhock. It occurs upon 
any green part of the plant. On the leaves it forms brown 
spots and causes withering; upon young succulent petioles or 
stems, collapse of the parts beyond follows; if the parts be 
older, sunken spots varying from light yellow to black are 
produced. 

The plants should be sprayed with Bordeaux mixture as 
soon as the first leaves appear and every second day there- 
after. 

Angular leaf-spot (Septoria) is also common. 



Ornamental Plants 425 



HYDRANGEA 



Leaf-spot (Phyllostida hydrangece E. & E.). — Large, 
rusty, brown blotches occur upon the leaves, in some 
cases to such extent that the tops of the plants must 
be cut awa3% to the entire destruction of their decorative 
value. 

Rust {Pucciniastrum hydrangece (B. & C.) Arth.) is common 
and often serious. 

Leaf-spot {Cercospora sp.). — Small, round, or angular 
white spots with a very small amount of dark hyphal 
growth in the centers are common upon this plant. The 
spots are definit^e and are bordered by a narrow reddish 
purple Hne. 

IRIS 

Leaf-spot ''-^ (Didymellina iridis (Desm.) v. H., Heterospo- 
rium). — The disease occurs only on the German iris, affect- 
ing mainly the upper portion of the leaf with oval spots with 
water-soaked margins. Dead leaves should be removed as 
soon as the snow melts away. 

IVY {Hedera) 

Blight {Vermicularia trichella Fr.). — This blight usually 
begins midway between base and apex of the leaf, and is 
especially common upon the white portions of the variegated 
varieties. The diseased portions turn black, and small black 
acervuli appear. 

LAUREL, MOUNTAIN (Kalmia) 

Leaf -blight {Phomopsis kalmice Enl.). — Dead spots ap- 
pear on the leaves and may involve the entire blade, later ex- 
tending to the stems and even killing entire plants. Leaf- 
spot {Septoria kalmicola (Schw.) E. & E.) is of common 
occurrence. 



426 Diseases of Economic Plants 

LARKSPUR 

A black leaf-spot due to bacteria has been noted in Massa- 
chusetts. 
Drop (Sclerotinia) . — See lettuce. 

LILAC 

Powdery-mildew (Microsphoera alni (Wallr.) Salm.). — 
The characteristic spots of the powdery-mildew, white and 
flour-Hke, are frequent upon the lilac. Black perithecia are 
abundant late in the season. 

Leaf-spot (Bacteria) is of minor consequence. 

LILY 

Gray-mold ^"'^ {Dotrytis sp.). — This exceedingly destruc- 
tive mold of the lily was noted about 1885, and was first 
closely studied by Ward in 1888. It makes its appearance 
in the spring as small, orange-colored spots upon the leaves 
and buds. These enlarge, and later become coated with a 
light brown, dusty, fuzzy mold which destroys the leaves and 
blossoms, often leaving only the naked stalks standing. 

Sclerotia much like those described under lettuce drop 
appear in association with the decay in its late stages. Their 
subsequent history is like that of lettuce sclerotia. 

Bermuda lily-disease. ^^^ — The plants are stunted and the 
leaves are distorted and bear spots that are yellowish to white 
and usually sunken. Frequently a commercial loss of from 
20 to 60 per cent follows. No parasite is present, and the 
actual cause of the disease is unknown. Rogueing in the 
field to eliminate affected bulbs is necessary. 

LILY-OF-THE-VALLEY 

Drop {Sclerotinia sps.). — See lettuce. 

MIGNONETTE 

Leaf-spot ^^"^ {Cercospora resedce FcL). — This disease 
occasionally ruins the greenhouse crop. The spots are at 



Ornamental Plants 427 

first minute, pale, with brownish or yellowish borders, or 
they spread over the leaf as a reddish discoloration. In 
late stages they are uniformly brown, with dark hyphae 
scattered over the central portions. The dead areas enlarge 
irregularly, and the leaves finally curl and die. 

Bordeaux mixture and ammoniacal copper carbonate, used 
once a week, have proved effective remedies. 

MORNING-GLORY, MOON-FLOWER 

The following are common but usually not serious: 

Rust (Coleosporium ipomoece (Schw.) Burr.); White-rust 

(Albugo ipomoece-pandurance) ; Leaf-spots due to various 

fungi. 

NASTURTIUM (Tropoeolurn) 

Blight {Pseudomonas aptaium). — In this disease the leaves 
are wilted and bear water-soaked spots usually about 3-5 
mm. in diameter. Black-mold (Pleospora tropoeoli Hal., 
AUernaria). — The leaves which are affected turn light green, 
later yellow, and still later are covered with a black mold. 

Damping-off (Colletotrichutn). — Damping-off due to a 
species of Colletotrichum is common in the cutting-bed. 
The diseased parts bear numerous black acervuli. 

White-rust (Albugo Candida) occurs rarely. 

OLEANDER 

Knot, gall '*''''' (Bacillus). — This disease both upon leaves 
and stems appears to be identical in character with that upon 
the olive. 

ORCHIDS 

Mold (Botrytis). — The presence of straw-colored spots 
often renders the plants unsightly and the flowers valueless. 
A gray mold similar to that found upon the lily appears later. 

All infested refuse should be burned. 



428 Diseases of Economic Plants 

Numerous anthracnoses, leaf-spots, rusts, and other dis- 
eases also occur on orchids. Their discussion would involve 
many pages. See also, p. 412. 

PALM 

Anthracnose {Colletotrichum) . — Palms often die and turn 
black at the tips of the leaf segments, or similar spots may 
appear upon other parts of the leaf. These spots near their 
edges have a watery appearance. When they become dry, 
purplish acervuli appear. Upon seedlings the disease is par- 
ticularly troublesome, resulting in failure of the leaves to 
unfold. 

The blighted parts should be cut away and burned and the 
remaining foliage sprayed at least once each week with 
Bordeaux mixture or ammoniacal copper carbonate. 

Graphiola blight {Graphiola phmnicis (Mong.) Poit.). — 
Small, gray, tubercular growths, 1-2 mm. in diameter, appear 
scattered over the leaves. In greenhouses the disease is 
commonly present but not in destructive form as it is further 
south in the open. Numerous other leaf-spots also occur on 
the many varieties of palms. 

PANSY. See violet. 

PEONY 

Mold 448 (Botnjtis). — This mold was first noted in 1897 in 
Europe. It has since been reported in Canada, Massachu- 
setts, Rhode Island, Pennsylvania, and Maryland as causing 
serious loss. 

Young plants are attacked almost as soon as they appear 
above ground, and ashen gray spots are produced upon the 
bud-scales, and stems. Among older plants the rot develops 
upon the leaves, unopened buds, and at the base of the stem. 
Brown mold similar to that described for lettuce not in- 
frequently develops upon the affected parts. Numerous 



Ornamental Plants 429 

greenish-black, flat sclerotia, 1-13^ mm. in diameter, are 
formed in the stems. 

Dead leaf and stem remains should be removed from the 
peonies before they are set in the ground. Bordeaux mix- 
ture may be used after the plants appear in the spring. 
Infested beds should be steamed. Drop (Sclerotinia). See 
lettuce. 

PETUNIA 

Drop (Sclerotinia) . See lettuce. 

PHLOX 

Powdery-mildew (Erysiphe cichoracearum DC). — This is 
of general distribution and injurious. Leaf-spot (Cercospora 
phlogina Pk.). — Brown circular spots occur on the leaves. 

PINK 

Rust (Pucciriia arenarioe (Schm.) Schr.). — This rust was 
described in 1803 by Schumacher. It is quite common upon 
various members of the pink family, for example, chick- 
weeds, corn cockle, Bouncing Bet, etc. The sori are large, 
raised blisters arranged in characteristic concentric circles. 

Diseased plants should be burned. 

PRIMROSE 

Leaf-spot {Phyllostida primulicola Desm.). — Large, cir- 
cular, brown, dead spots are produced upon the leaves. 
Minute dark pycnidia may be seen. Leaf -spot {Ascochyta 
primulce Trail) . — Well-defined oval spots, resembling those 
of the phyllosticta leaf-spot, are formed. These two diseases 
cannot be distinguished without the aid of the microscope. 
Leaf-spot {Ramularia primulce Thuem.). — In this disease 
the blotches are yellow with centers of ashen whiteness. No 
pycnidia are present, but instead a gray coating of mold. 
Anthracnose (Colletotrichum primulas Hal.). — In this blight 



430 Diseases of Economic Plants 

the entire leaf is more often involved than in the above 
diseases, and definite spots are more rare. Dark acervuli are 
present. 

Gray-mold {Botrytis sp.). — This occurs upon leaves and 
flowers much as upon lettuce. 

Bordeaux mixture is useful with all of these primrose 
diseases. 

PRIVET 

Anthracnose ^"^ {Glomerella cingulata, Gloeosporium) . — 
Twig blight superficially resembling that of the pear is a 
character of this disease in its later stages, terminal parts of 
the twigs 2-5 cm. long being affected. The line of separation 
between diseased and healthy tissue is sharp through shrink- 
ing and depression of the diseased part. In early stages de- 
pressed, oblong, diseased spots, at first very minute, are seen 
upon the bark. These spots enlarge, eventually girdle the 
twig, and cause the death of the distal part. Minute black 
elevated acervuli, visible to the naked eye, are scattered over 
the surface of the original disease spots. 

Affected branches should be cut well below the diseased 
portion and burned. A spring spraying, before the buds 
swell, with any good dormant spray will still further reduce 
infection. 



ROSE 



466 



Black-spot ^''^ (Diplocarpon rosce Wolf, Adinonema) . — 
Both in and out of doors, this is a widely known and destruc- 
tive rose disease. It was first described in 1824, and is now 
widely distributed throughout Europe and the United States. 
It consists of irregular circular or oval indefinitely bordered, 
black spots upon the upper surface of leaves that are mature 
or nearly so. The larger spots are a centimeter or more in 
diameter, and they frequently coalesce so as nearly to cover 
whole leaflets. 

With age the spots turn gray at the centers, at which part 



Ornamental Plants 



431 



the leaf dies. They also become more regular in outline than 
in their earlier stages. Portions of the leaflets outside of the 
area actually spotted often turn yellow, and the diseased 
leaflets fall off prematurely. Thus the beds beneath diseased 
plants are often strewn with fallen leaves. 

All infective material should be gathered and burned, and 
by use of a good dormant spray both bushes and ground be 




Fig. 220. — Rose mildew; diseased and healthy shoots. 



well cleared of superficial spores. Ammoniacal copper car- 
bonate used once each week is effective after the plants are in 
foliage. Lime-sulfur or Bordeaux mixture may be used 
when the residue on the foliage is not objectionable. 

Powdery-mildew {Sphcerotheca pannosa (Wallr.) Lev. or 
S. humili (DC.) Burr, Oidium). — This is perhaps the most 
wide-spread and destructive of all rose diseases both under 
glass and in the open, being especially destructive to the 



432 Diseases of Economic Plants 

rambler varieties. In mild cases it occurs merely as flour-like, 
dusty white patches upon the leaves. But when present, it 
usually becomes aggressive, attacking the young leaves and 
tender shoots, which become dwarfed, curled, reddened, va- 
riously deformed (Fig. 220), and covered with the white 
powder of spores and spore stalks. The vitality of the plant 
is so lowered by repeated attacks and even by direct attack 
upon the buds that the plants become worthless. 

Indoors sulfur is serviceable. The house should be 
closed and the sulfur boiled in a kettle for two to three 
hours twice weekly, or the house may be closed in the morn- 
ing, the temperature raised to 24° C. (75° F.), and the air 
well filled with sulfur from bellows. The temperature 
should then be raised to 31°-32° C. (85°-90° F.), and al- 
lowed to cool gradually. 

Either out doors or in, dusting (sulfur 90 parts, arsenate 
of lead 10 parts) is effective and more convenient than 
spraying with Bordeaux mixture or lime-sulfur. 

Canker '^^^ {Cylindrocladium scoparium Morg.). — Brown, 
dead cankers are formed on the stems and branches, or at the 
crown, and often encircle the stem for several centimeters. 
Considerable injury is done to roses under glass. Examine 
new stock carefully to exclude canker. If the disease enters 
the house remove all old soil and disinfect the benches with 
formalin. Brown-canker ^^^ {Diaporthe umbrina Jenk., 
Phomopsis) also occurs on roses of many varieties. 

Rust {Phragmidium suhcoriicum (Schr.) Wint.). — This 
true rust is common in Europe, and is found in many parts 
of the United States from the Atlantic to the Pacific; still 
it is not a very serious pest. 

Early in the season orange-yellow sori appear upon the 
green parts of the plant: on the leaf as small, circular spots; 
on the stems and petioles often as quite large, powdery 
masses. Later in the season the color of the sori changes 
to brick red. 

Affected branches should be burned promptly, and all 
infective material should be burned in the autumn. If 



Ornamental Plants 433 

the disease reappears, the whole plant should be dug up 
and burned. In beds where the disease has occurred, a 
dormant spray should be applied in early spring. Another 
rust is due to Earlea speciosa (Fr.) Arth. — Though much like 
the last, this is limited in its attack to the stems, rarely 
petioles. The sori are irregular and black. Since the causal 
fungus is perennial in the stems, excision and burning are to 
be practiced. 

Anthracnose {Gloeosporium rosce Hal.). — This anthrac- 
nose is very similar to that of the raspberry. The diseased 
canes, bearing small, pale leaves, die from the tip backward 
for 2-3 dm., and red acervuli appear upon them after death. 
Often the canes become completely defoliated. 

Affected plants should be sprayed with Bordeaux mix- 
ture or ammoniacal copper carbonate. 

Leaf-spot (Mycosphcerella rosigena E. & E.). — The leaves 
are marked with gray, irregular, indefinite blotches which 
bear minute black perithecia in their centers. Another 
leaf-spot is due to Cercospora rosceicola Pass. Circular, gray 
spots bordered with dark purple but without pycnidia are 
present. 

Downy-mildew (Peronospora sparsa Berk.). — This mil- 
dew is kin to that of the grape. Its spots are indefinite, and 
the characteristic, downy, white to purple coating is noted 
upon the lower surfaces of the leaves. It is not common in 
America. Bronzing, its name indicating its character, 
occurs frequently. It is not due to parasites and does no real 
harm. 

Crown-gall. See peach. 

• 

SEDUM 

Leaf-spot {Septoria sedi West.). — Dark, circular blotches 
appear upon the leaves and result in such defoliation that the 
stems often become naked nearly to the tips of the branches. 
Infected parts should be burned. Anthracnose (Vermicularia 
telephii Karst.). — This disease usually appears first at the 



434 Diseases of Economic Plants 

point of attachment of the leaves, and later it passes to the 
stem, causing soft rot and shrinking of the outer parts. After 
defoliation the disease spreads slowly toward the base of the 
stem. Infected parts should be burned. 

SNAPDRAGON 

Anthracnose ^■''^ (Colletotrichum antirrhini Stew.). — -This 
disease which often ruins the crop is the most destructive of 
this host, both under glass and in the open. It attacks plants 
of any age, producing on the stem elliptical sunken spots, 
5-8 mm. long, and on the leaves circular dead spots. These 
are at first dirty white with narrow brown margins; later 
acervuli appear in the center, at first brown, then black. 
Diseased plants show numerous, dead, hanging leaves. The 
stems or lateral shoots may be girdled, killing the parts 
beyond. 

It is recommended to use only healthy plants for cuttings 
and to clean up and burn all diseased refuse. The cuttings 
should be sprayed when well rooted and repeatedly until 
transplanted. Excess of water should be avoided and 
thorough ventilation provided. 

Leaf-spot '""-^ {Phyllosticta antirrhini G. & A.). — Circular, 
brown or black spots about one centimeter in diameter, 
usually marked by concentric ridges, appear on the leaves. 
Lesions on the petioles cause death of the leaf and infection 
of the axils. Stem lesions may be 2 or 3 cm. long and 
eventually girdle the stem, resulting in death of all distal 
parts. Young plants die from typical damping-off. Bor- 
deaux mixture is recommended for forms of the disease 
other than damping-off, which must be met by soil dis- 
infection. 

Rust ''^^ (Puccinia antirrhini D. & H.). — This rust has 
recently appeared in greenhouses in destructive form. Dis- 
eased stock should be excluded and sub-irrigation adopted if 
possible. 



Ornamental Plants 435 



SPURGE 



Anthracnose (Gloeosporium euphorhice Hal.)- — The attack 
usually begins upon the flower cluster and passes down the 
stem to the leaves, which then fall away, leaving the naked, 
blighted branches. The disease often interferes seriously 
with the ornamental effect of this decorative plant. 

SUNFLOWER, JERUSALEM ARTICHOKE 

Rust {Puccmia helianthi Schw.). — Both wild and cul- 
tivated species of sunflowers are often badly rusted. The 
early sori are yellow to brown, the later black. Badly rusted 
leaves die and much injury follows both to flower and seed. 
In the spring the cluster-cup stage is sometimes found upon 
the same host. Burning of infested refuse is the only remedy 
known. 

j)j-Qp 455 (^Sclerotinia perplexa Law.). — The disease ap- 
pears first in the root or lower stem and spreads upward to 
the heads. It in general character resembles lettuce drop. 
Leaf -spot {Septoria helianthi E. & K.) is common but not 
serious. 



SWEET-PEA 



454 



Anthracnose (Glomerella cingulata, Gloeosporium) occurs as 
spots on stems, leaves, and pods. Seed from diseased pods 
should be avoided. 

Powdery-mildew {Microsphcera aim, Oidium) . — This is 
not usually troublesome if proper greenhouse conditions are 
maintained. See rose. 

Streak {Bacillus lathyri M. & T.). — Dark streaks occur 
on the stem. Wilt (Fusarium). — See cowpea wilt. Drop 
{Sclerotinia) . — See lettuce. Mosaic. — See tobacco. Root- 
rots are numerous, due to Nematodes, Thielavia, Corticium, 
and other fungi. 



436 Diseases of Economic Plants 

TULIP 

Gray-mold (Botrytis) . — All parts of the host except the 
roots are affected. The disease was apparently imported 
from Europe and is now established throughout the United 
States. 

VERBENA 

Powdery-mildew (Erysiphe cichoracearum DC, Oidimn). 
— Powdery-mildew is quite common upon verbena under 
glass or in the open. 

The use of potassium sulphid, 1 ounce to 3 gallons, twice 
a week has proved effective. 

VINCA 

Rust (Puccinia vincce (DC.) Berk.) was apparently im- 
ported from Europe and does occasional damage. Vinca 
leaf-spot {Sphceropsis vincce Sacc.) occasionally injures leaves 
and stems. 

VIOLET, PANSY 

Spot-disease ^-^^ {Alternaria violce G. & D.). — This is one 
of the widespread and destructive violet diseases. It attacks 
the plant at any stage of its growth and upon any green part, 
but is most destructive upon the foliage. It first appears as 
small, definite, circular, greenish or yellowish-white spots, 
varying from mere dots to 1 mm. in diameter. The light cen- 
ter is surrounded by a narrow ring, usually dark brown to 
black, but turning lighter with age. As the spot enlarges the 
freshly diseased tissue is usually watery and translucent, 
and the center changes to yellow or gray-white and may 
fall out. Frequently by the combined effects of several 
spots the whole leaf is destroyed. If the air is damp, a 
thin coating of rusty-colored spores may be seen in the old 
spots. 

Damp, warm, cloudy, summer weather, unclean houses, 



Ornamental Plants 437 

weak plants, poor stock, poor beds, are predisposing con- 
ditions to disease. 

To avoid the disease the houses shoukl be kept scrupu- 
lously clean, only strong stock used, infested material picked 
and burned, and insects banished. Close attention must 
also be given to ventilation, heating, shading, and watering. 
The soil should be removed each season and every means 
used to produce strong resistant plants. Other leaf-spots are 
due to Cercospora violce Sacc, Phyllosticta violce Desm. and 
Marssom'na violce (Pass.) Sacc. No pycnidia are present, but 
the centers of the spots are darkened by the presence of 
hyphse. 

Anthracnose "^^^ (Colletotrichum violce-iricoloris RES.). — 
This blight has been noted in many states. It is characterized 
by the appearance of dead, black-bordered spots on the 
leaves and petals, thus disfiguring the flowers, and affecting 
the production of seed, or even bringing premature death 
to the plant. 

Thorough and frequent spraying with Bordeaux mixture 
is advocated. 

Wilt ^^'^ (Fusarium violce Wolf). — This was noted as of 
economic importance in Nebraska, where it caused sudden 
dying of apparently healthy plants. Slightly sunken areas 
were evident on the stems just above the ground, and the 
roots were reduced to mere stumps. 

Rust (Puccinia violce (Schm.) DC). — One of the most 
common of pansy diseases is this true rust which affects all 
aerial parts of the plant. It is recognized by its sori. 

Downy-mildew (Peronospora violce De Bary). — The 
downy-mildew is in general character like that of the grape. 
The spots are indefinite, and affected plants droop and die. 

Anthracnose {Glceosporium violce B. & Br.). — The an- 
thracnose often begins at the edge of the leaf, as an irregular 
discoloration which extends inward, eventually blighting the 
whole leaf. 

Root-rot {Thielavia). — Affected plants are stunted and 
yellow. The underground parts show numerous dark spots 



438 



Diseases of Economic Plants 




Fig. 221. — Violet leaves, healthy and affected by spot-disease. 

After Dorsett. 



Ornamental Plants 439 

of dead tissue which often involve the roots for considerable 
distances. The disease is the same as that of tobacco. Root- 
rot (Corticium), see p. 21. 

Mold {Zygodesmus albidus E. & H.). — This mold forms a 
white, flour-like coat over the leaf. 

VIRGINIA CREEPER (Ampelopsis) 

Leaf-spot {Guignardia hidivellii, Phyllosticta) . — The spots 
occurring upon the leaves and shoots are identical in ap- 
pearance with those upon the grape, and the same treatment 
is recommended. 

Powdery-mildew. See grape. 

Stem-rot {Cladosporium herharum Lk.). — Large blanches 
or even the entire plant may be killed. 

WATER-LILY 

Leaf-spot (Cercospora) . — Circular spots, at first pale 
green, later yellow, and finally brown and dead, are produced 
upon the leaves. The dead tissue may break away, leaving 
irregular holes. 

Soda-Bordeaux mixture is recommended, since it is effec- 
tive and does not spot the leaves. It is beneficial also in 
removing undesired algal growth. Another leaf-spot is due 
to Helicosporium nymphcearum Rand. — Dark spots often 
red-bordered occur on the leaves and may enlarge to involve 
the whole leaf. 



FUNGICIDES* 

Bordeaux mixture. ^^4' ^^''' ^^^^ ^^^^ '^^^ — The 4-4-50 formula 
(4 pounds of copper sulfate crystals and 4 pounds of stone- 
lime to 50 gallons of water) is one in common use. 

According to the common formulas several times as much 
lime is used as is necessary to precipitate the copper. A 
mixture used abroad, known as the Woburn mixture, calls for 
a solution of copper sulfate with lime water and subsequent 
dilution as contrasted with milk-of-lime used in the ordinary 
Bordeaux mixture. According to Pickering ordinary Bor- 
deaux mixture and the Woburn mixture, containing only 
one-sixth as much copper, seem to be equivalent in fungicidal 
action. 

To make large quantities of Bordeaux mixture, or small 
amounts repeatedly, it is desirable to prepare separate con- 
centrated stock solutions of copper sulfate and of lime. 
These are made up at the rate of approximately one pound 
of each to the gallon. In preparing a stock solution of 
copper sulfate, a weighed amount of the commercial crystals, 
''bluestone, " is placed in a sack and suspended in water in a 
barrel or other wooden vessel. The volume of the water 
should equal in gallons the weight of the copper sulfate in 
pounds. The solution, as formed, will flow to the bottom, 
leaving comparatively fresh water in contact with the re- 
maining crystals. Stirring partially defeats the purpose of 
this method by increasing the concentration of copper 
sulfate in the liquid in contact with the undissolved part. 
If the copper sulfate is placed in the bottom of the barrel, it 
will dissolve but slowly even with frequent stirring. When 
dissolved, the solution should be made uniform by stirring. 

In preparing the stock solution of Hme (the term in com- 

* Prepared by W. A. Ruth. 
440 



Fungicides 



441 



mon use in this connection for a suspension of calcium hy- 
droxid) a definite quantity of fresh stone-lime is placed in a 
trough, slaked, and made up to a volume corresponding in 
gallons to the weight of the lime in pounds. In slaking the 
lime a small quantity of water is used to start the reaction, 
and just enough water is added, as the lime slakes, to prevent 
crumbling. The lime and water are stirred from the time the 
lime starts to slake until the reaction appears to be complete. 




Fig. 222. — A convenient arrangement for mixing Bordeaux 
mixture. After Vermont Agr. Exp. Sta. 

Instead of diluting to the final volume at this point, it is 
somewhat desirable to add just enough water to prevent 
drying out and to allow the mixture to cool before the further 
addition of water. This procedure permits further slaking, 
which results in a noticeably creamier stock solution, with 
fewer particles of unslaked lime to clog the nozzles. 

The common method in use in making Bordeaux mixture 
in the field has been to dilute the required quantities of 
copper sulfate and lime separately to half the final volume 



442 Diseases of Economic Plants 

required and to pour them together into a separate con- 
tainer, usually the tank of the sprayer. The colloidal sus- 
pension obtained by this method of mixing settles very 
slowly and can be applied with the maximum uniformity. 
To make 200 gallons, the content of the usual power sprayer, 
by this method, an elevated platform, or a series of elevated 
platforms, is required. The diluted lime and copper sulfate 
are run simultaneously from 100-gallon wooden contain- 
ers standing on the platform into the sprayer, or into an 
elevated 200-gallon tank, where the resulting Bordeaux 
mixture is held in readiness to supply the power sprayer 
while the smaller containers are being refilled. 

The above method is open to improvement because of the 
large amount of apparatus and labor involved. 

Hawkins claims "a Bordeaux mixture in which the sus- 
pension of the copper compound settles out slowly may 
be prepared by adding the concentrated calcium hydroxid 
to the diluted copper sulfate solution or vice versa, pro- 
vided the mixture is sufficiently agitated." He states that 
*Hhe agitation necessary for preparing Bordeaux mixture 
with a low rate of subsidence by this method could hardly be 
obtained in practice except by means of a power outfit pro- 
vided with a good agitator." This method can be used to 
advantage with the tank-filler, a jet pump, with which 
any power sprayer can be equipped, which permits the rapid 
filling of the spray tank by means of the spray pump. The 
construction of a platform and the expense of pumping water 
into the elevated containers are thereby obviated. Sixteen 
gallons of stock copper sulfate or lime is first diluted in the 
spray tank to within sixteen gallons of the final volume, the 
stock solution of the other component is poured in, and the 
mixture is thoroughly agitated. A method very similar to 
this has proved satisfactory in the field and is in common use 
in Illinois. 

Wooden containers should always be used for the copper 
sulfate solutions, and the lime or Bordeaux mixture, should 
always be strained before it enters the tank. 



Fungicides 443 

Lime-sulfur.''^^ — This fungicide (the material is also 
used in the control of San Jose scale) is prepared by boiling, 
in water, lime and sulfur in the proportion of approximately 
two parts of sulfur to one of lime. The products in the 
resulting solution are calcium thiosulfate (CaS203), calcium 
tetrasulfid (CaSi), and calcium pentasulfid (CaSs). The 
material may be made by the orchardist or bought from 
manufacturers. The commercial product is more concen- 
trated than that made by the formulas usually recom- 
mended for home use, and contains a higher proportion 
of polysulfid sulfur (that is, sulfur in the form of CaS4 
and CaSs). 

The combination of constituents ^^^ that appears best to 
meet the largest number of desirable conditions is the follow- 
ing, stated in round numbers: 

36 pounds of lime (pure lime, CaO, used as a basis). 
80 pounds of high grade, finely divided sulfur. 
50 gallons of water. 

When lime containing impurities is used, more than 36 
pounds must be taken in order to obtain 36 pounds of pure 
lime. 

Use 38 pounds of lime containing 5 per cent of impurities 
(95 per cent pure). 

Use 40 pounds of lime containing 10 per cent impurities 
(90 per cent pure). 

No lime should be used which contains more than 10 per 
cent of impurities. If the lime contains impurities (oxid of 
magnesium, iron, aluminum, etc., and carbonates of mag- 
nesium, calcium, etc.), these do not go into solution but re- 
main as sediment, together with any undissolved sulfur 
not acted upon because of insufficiency of pure lime, due to 
impurities in the lime used. The amount of sediment thus 
formed can be utilized as a measure of the amount of im- 
purities existing in the lime. 

The level of the mixture during boihng should be kept near 
the 50-gallon mark — not being allowed to drop more than an 



444 Diseases of Economic Plants 

inch below — this regulation is accomplished by adding water 
from time to time in the required amounts. It is preferable to 
add water in small amounts at frequent intervals rather than 
larger amounts less often, since the boiling is less interrupted. 
When the boiling is completed, the level of the liquid should 
be made up to the 50-gallon mark, if not already there. 
It will be found to have a density of 24° to 25° Baume when 
cooled to about 16° C. (60° F.). 

One gallon of this solution may be diluted with 25 gallons 
of water for summer use as a fungicide. Commercial solu- 
tions, which usually test about 33° Baume, may be diluted 
with 40 parts of water. The degree of dilution has relatively 
slight effect, however, upon the fungicidal properties of the 
solution, in comparison with the effect of thoroughness of 
application, and the amount of dilution may vary within 
wide limits. 

Another method for making lime-sulfur consists in the 
use of live steam, furnished by a boiler, and led into wooden 
barrels or tubs, in which the mixture is boiled (Fig. 223). 
Large tubs provided with mechanical agitators are sometimes 
used. Less water is needed than is called for by the formula 
given above, because of the condensation of the steam used in 
heating. 

Self-boiled lime-sulfur wash. — The self-boiled lime- 
sulfur wash is a combination of lime and sulfur boiled 
with only the heat of the slaking lime, and is primarily in- 
tended for summer spraying of peaches. Peach foliage is so 
susceptible to spray injury that ordinary Bordeaux mixture 
cannot be used as a summer spray; neither can the sulfur 
washes which contain any considerable quantity of sulfids 
in solution. The self-boiled lime-sulfur wash, however, 
when prepared as a mechanical mixture of lime and sulfur 
with only a small percentage of the sulfur in solution, is not 
injurious to peach foliage and has proved to be a good fun- 
gicide. 

The mixture that appears to be the most satisfactory is 
composed of 



Fungicides 445 

Lime 8 pounds 

Sulfur 8 pounds 

Water 50 gallons 

This can best be prepared in rather large quantities — 
16 pounds, or even 32 pounds at a time — so as to get enough 
heat to produce a violent boiling for a few minutes. Place the 




Fig. 223. — Making lime-sulfur wash. After Sherman. 

lime in a barrel and pour on enough water (about 3 gallons to 
16 pounds) to start it slaking and to keep the sulfur off the 
bottom of the barrel. Then add the sulfur, which should 
first be worked through a sieve to break up the lumps, and 
finally enough water to slake the lime into a paste. Con- 
siderable stirring is necessary to prevent caking on the bot- 
tom. After the violent boiling which accompanies the slaking 
of the lime is over, the mixture should be diluted ready for 
use, or at least enough cold water added to stop the cooking; 



446 Diseases of Economic Plants 

5 to 15 minutes, according to whether the Hme is quick-acting 
or sluggish, are required for the process. At the end of 30 
or 40 minutes, if the hot mass is permitted to stand undiluted 
as a thick paste, a liquid is produced that is dangerous to 
peach foliage and in some cases even to apple foliage. 

The mixture should be strained through a sieve of 20 
meshes to the inch in order to remove the coarse particles 
of lime, but all the sulfur should be worked through the 
strainer. 

Hot water may be used to good advantage in preparing 
the mixture with sluggish lime, but with quick-acting lime 
hot water is not best. The mixture may be kept for a week 
or more without deterioration, but it should be thoroughly 
stirred before using. 

In applying the self-boiled lime-sulfur wash the spray- 
ing outfit should be equipped with a good agitator. The 
agitator of the ordinary barrel sprayer is not usually ade- 
quate. 

Sulfur-dust. ^^^' ''^^' ^^"' ^^^' ^^- — Very favorable reports have 
appeared recently of the results secured by the use of sulfur 
dust as a fungicide for apple scab in New York. Results 
obtained by experiments carried on further south have not 
been favorable to its use for this purpose. Thus Giddings 
states that as the result of four years' trial it can not be 
recommended for use on apples where scab or sooty blotch is 
severe, or for the treatment of bitter-rot, black-rot, or blotch. 
Brock finds in Illinois that spraying is much superior to 
dusting for the control of fungi, but believes that in favored 
localities, where fungi are comparatively easy to control, the 
sulfur dust has its uses. 

Reddick and Crosby recommend, for the average Western 
New York conditions, a mixture containing 85 per cent of 
exceedingly finely ground sulfur (especially ground, ''super- 
fine") and 15 per cent of dry arsenate of lead (the ''fluffy" 
sort is used for this purpose). The exact quantity of mate- 
rial to be used per tree will be determined by the wind, 
the size and the shape of the trees, and also by the thorough- 



Fungicides . 447 

ness of distribution effected. From 1.25 to 2.5 pounds are ap- 
plied per tree in each application. '^ In localities where apple 
scab is less abundant than in the lake counties, as seems to be 
the case in most of the Hudson River section, the quantity of 
sulfur applied per tree may be reduced. It would be well, 
however, to regard these as minimum amounts until expe- 
rience has shown that they can be reduced with safety." 

Dusting appears to be slightly more expensive than spray- 
ing. The cost of materials is higher, but this factor in the 
total cost is partiall}^ overcome by the lower cost of applica- 
tion. The chief advantage in dusting, however, lies in the 
extreme rapidity with which the dust can be applied. This 
appears to permit the application of the fungicide at periods 
when the weather conditions favor infection with apple scab, 
and to result in comparative flexibility in the spray schedule. 

Ammoniacal solution of copper carbonate. — This solution 
contains no sediment, and on drying leaves no unsightly 
marks. It may therefore be used when the spotting that 
the Bordeaux mixture causes precludes the use of that 
fungicide. The mixture consists of a solution made by dis- 
solving copper carbonate in ammonia-water in the following 
proportions : 

Copper carbonate 6 ounces 

Ammonia, about 3 pints 

Water 50 gallons 

Weigh out the proper amount of copper carbonate. Set a 
very small portion of this aside, and dissolve the remainder 
of it in diluted ammonia, using only enough ammonia to 
dissolve it. Then add the portion of copper carbonate which 
was reserved. This will insure the use of no more ammonia 
than is necessary. It is better to have a little too much of 
the carbonate in the solution than to have too much ammonia. 
The strong solution made in this way can be diluted with the 
proper amount of water. The copper carbonate may be 
purchased directly from the drug-store, or it may be prepared 
at home. 



448 . Diseases of Economic Plants 

To make copper carbonate proceed as follows: Dissolve 
10 pounds of copper sulfate in 10 gallons of water. Also 
dissolve 12 pounds of carbonate of soda in the same amount of 
water. Allow these two solutions to cool, then mix them 
slowly together, stirring in the meantime. Allow the mixture 
to settle about 12 hours, pour off the liquid, and add water 
equal in amount to the liquid poured off. Stir thoroughly 
and allow it to settle as before. Repeat this operation again, 
then drain off all the liquid possible, and dry the blue powder 
which remains. This powder is the copper carbonate. 

Burgundy mixture. 

Copper sulfate 2 pounds 

Sodium carbonate (sal soda) 3 pounds 

Water 100 gallons 

Each chemical should be dissolved separately in half 
the water, then mixed as in making Bordeaux mixture. 
This mixture may be used, as may ammoniacal copper 
carbonate, when it is advisable to avoid the spotting of 
fruit which would result from use of the Bordeaux mixture. 

Copper sulfate solution, 1-17. — A solution consisting 
merely of copper sulfate and water to kill spores on the 
bark and supports may be used before the leaves appear. 

Dissolve the copper sulfate as in preparing the Bordeaux 
mixture, dilute it to the required strength, and spray upon the 
trees. The addition of a little lime, one half pound to 50 
gallons of mixture, enables the operator to see exactly what 
portions of the tree have been sprayed. 

This mixture must not be used after the leaves appear. 

Potassium sulfid solution. 

Potassium sulfid (liver of sulfur) 1 ounce 

Water 2 to 4 gallons 

This solution should be freshly prepared. It is used as a 
substitute for the Bordeaux mixture, to avoid spotting, in 



Fungicides 449 

the same way that the ammoniacal sohition of copper car- 
bonate is used. Potassium sulfid is also especially efficient 
as a protection against the powdery-mildews. 

Formalin. — Formalin is a very powerful germicide which 
came into wide use about 1889. Its interest to the farmer 
lies chiefly in its power to prevent the potato scab, onion 
smut, and the various smuts of cereals. Full directions for 
its use are given under special crops. 

This substance appears on the market under two names: 
'' Formalin" and ''37 per cent formaldehyde." These sub- 
stances are absolutely identical, and since the formaldehyde 
solution is cheaper, owing to the fact that the word "For- 
malin" is protected by patent, the customer will of course do 
well to purchase the 37 per cent solution. 

Corrosive sublimate. 

Corrosive sublimate 1 part 

Hydrochloric acid 2 parts 

Water 1000 parts 

This is employed chiefly as a seed disinfectant particu- 
larly for black-rot of cabbage. It is intensely poisonous 
and should be so regarded. 

Flowers of sulfur. — This substance is chiefl}^ employed 
as a specific for the powdery-mildews. See grape, p. 122. 

Proprietary fungicide s.^^^ — There are several proprie- 
tary fungicides on the market. Of five tested on apples 
in 1916, at the Illinois Experiment Station, four produced 
serious foliage injury and more or less serious injury to fruit. 
There are several commercial Bordeaux pastes on the market. 
Wallace has shown that none which he tested remains in 
suspension as well as fresh home-made Bordeaux mixture 
(some are very poor in this respect) and that they are very 
expensive if diluted to contain a copper content equal to that 
of 4-4-50 Bordeaux mixture. 

Combined fungicide and insecticide. — When an insecti- 
cide and a fungicide are to be used at the same time, it is 



450 Diseases of Economic Plants 

usually possible to combine the two so that only one applica- 
tion is necessary. The stomach poison which is commonly 
used for spraying tree fruits is lead-arsenate. It comes in two 
forms, the powder and the paste. The latter contains 50 per 
cent of water. The powder should be the fluffy, finely di- 
vided kind. Either form may be used with Bordeaux mix- 
ture or boiled or self-boiled lime-sulfur. The powder is used 
at the rate of 1 pound to 50 gallons of spray, the paste at 
the rate of 2 pounds to 50 gallons. 

Paris green can not be used with lime-sulfur, at least in 
spraying tree fruits, because of the resulting foliage and fruit 
injury. When used with Bordeaux mixture for spraying 
other plants it may be made up at the rate of 5 ounces to 
each 50 gallons of spray. 

Calcium arsenate seems to be a promising stomach poison 
for use with Bordeaux mixture or lime-sulfur. 

Nicotine preparations for the control of plant lice can be 
used with lime-sulfur, or with lime-sulfur and lead arsenate. 
There have been reports indicating that it should not be used 
with Bordeaux mixture. 

Bordeaux injury. ^^^' ''^"' ^^^ — Many plants sprayed with 
Bordeaux mixture assume a deeper color and are more 
vigorous and live longer than unsprayed plants, even in the 
absence of fungous attacks. The potato is a notable exam- 
ple. Other plants are injured to a greater or less extent. The 
peach, plum, sweet cherry, and apricot are so severely af- 
fected by Bordeaux mixture that this fungicide is not used in 
spraying them. 

Ever since the first trials of Bordeaux mixture upon the 
apple, some injury has been noted upon both leaves and 
fruit, due to the mixture itself. The amount of injury differs 
with different varieties and with other conditions. Water, 
deposited as rain or dew on the surface to which Bordeaux 
mixture has been applied, is a necessary contributing cause. 
As the season advances the foliage becomes more susceptible. 
On the other hand, the fruit is most susceptible early in the 
season. The most damage to the fruit occurs from the spray 



Fungicides 451 

applied just after the petals have fallen, and even the most 
susceptible varieties become almost completely immune 
within a period of six or ten weeks after this stage. 

On the fruit, injury is manifested by the formation of small 
black specks or the surface is russeted, sometimes very 
severely, and the fruit may be split or otherwise distorted. 
Injury to the foliage may first appear a few days after spray- 
ing or may be delayed for several weeks. Brown, dead spots 
are frequently caused, which may be followed by the yellow- 
ing and falling of the leaf. Yellowing may occur, however, 
when no brown spotting is observed. 

Before the discovery of the fungicidal properties of lime- 
sulfur and its efficiency as an early summer spray, various 
methods were suggested for the mitigation of Bordeaux in- 
jury. At present, lime-sulfur has very largely replaced 
Bordeaux mixture for use in the early summer. 

There are, however, circumstances under which Bordeaux 
mixture is still used at this season. It is generally conceded 
that lime-sulfur, applied with sufficient frequency, gives as 
good control of apple-scab as Bordeaux mixture, but that it 
is less adhesive and must be applied more frequently. Since 
the period when the trees are in blossom is sometimes pro- 
longed by adverse weather conditions, Bordeaux mixture is 
still consistently used by some fruit growers for the pre- 
bloom spray, on varieties locally subject to severe injury from 
scab. Bordeaux mixture may be used for the early blotch 
sprays on varieties not subject to Bordeaux injury, for all 
varieties in the control of bitter-rot and blotch after the 
period of immunity to serious Bordeaux injury has been 
attained, and of course for the entire program for varieties 
immune to this form of injury. 

Hedrick ^^^ has published an extensive list of apples classi- 
fied as to their immunity or susceptibility to Bordeaux in- 
jury. 

Lime-sulfur injury. ^^^-^^^ — Lime-sulfur injures many 
plants very seriously. Slight injury to the leaves of apples is 
of common occurrence. It is not usually of great consequence 



452 Diseases of Economic Plants 

or of a lasting nature. The injury consists of irregular brown 
spotting, especially where the spray accumulates immediately 
after its application. If, however, the leaves" have been 
injured by apple-scab, previous to the application of the 
spray, the damage done to the foliage is very serious. There 
is no marked degree of varietal susceptibility with apples. 
The injury occurs soon after the spray has been applied, not, 
as in the case of Bordeaux injury, at a period which may be 
long after its application. The foliage is least susceptible to 
injury soon after it has unfolded. Talbert states that the 
dormant spray consisting of commercial lime-sulfur, testing 
33° Baume, may be applied to apple trees diluted 1 to 7 or 
1 to 8 after growth starts and until the trees begin to bloom, 
without material injury to the leaves or flower buds. 
This is a much higher concentration than is usually used 
when the trees are in foliage. 

Lime-sulfur injury to the fruit occurs occasionally, as the 
result of drenching. It is generally conceded that injury 
to the fruit occurs if lime-sulfur is used in hot weather, 
after the fruit has developed to approximately the size at 
which it becomes relatively immune to Bordeaux injury. 
From this stage onward, Bordeaux mixture is again used, 
regardless of the foliage injury produced. Lime-sulfur injury 
may, however, result from the application made just after 
the petals fall or those just following. 



Spraying Apparatus 

Whether for spraying a small garden or a large commercial 
orchard proper apparatus is needed. 

The chief types of pumps are briefly mentioned be- 
low. 

Bucket pumps. — These pumps are suited for use in the 
garden; to spray the bushes or a few small fruit trees in the 
yard. The fact that they may be used in any ordinary 
bucket or pail gives them an advantage oyer some of the 
other outfits. By the attachment of a foot rest which ex- 



Fungicides 



453 



tends outside the pail to the ground, the pump can be held 
firmly. 

Compressed air sprayer. — After the tank is partly 
filled with the spray mixture and closed, air is pumped 
in, thus pressure is exerted upon the liquid, which is 




Fig. 224. — • Bucket pump 
showing hose, nozzle, 
and bucket attachment. 
After Gould Mfg. Co. 



Ficj. 225. — Barrel pump showing agitator. 
After Gould Mfg. Co. 



forced out in the form of a fine spraj' when the nozzle 
is opened. 

This type of sprayer is satisfactory in some instances, 
and is adapted to about the same fields as the bucket 
pump. It is not well adapted for spraying large areas, 
since the sprayers are inconvenient to carry, are slow and 
heavy. 



454 



Diseases of Economic Plants 



Knapsack sprayers. — These consist of 3 to 5-gallon 
tanks, with straps so attached that the outfit can be car- 
ried upon the back in the manner of a knapsack. The 
handle is so adjusted that it is operated in front of the 
carrier. These pumps are best adapted to spraying crops 
which grow breast high, as grapes. They may also be 
used in spraying small trees. For general garden use, 




Fig. 226. — ■ Modern power sprayer, equipped with high-pressure, 
slow-speed pump, with large bearings, ball valves, modern pressure 
regulator, etc. Such a machine is constructed to turn in a small 
space. A tower can be set on the tank for spraying tall trees with 
extension rods. 



or small areas, a half acre to an acre, they are to be 
recommended. 

Barrel pump. — For home orchard work the barrel sprayer 
is of most importance. The pump is adjusted to a 
barrel, at either the side or end. It should be provided 
with a good agitator to keep the spraying mixture stirred 
while in use. 

Field sprayers. — This sort of sprayer is used in spray- 



Fungicides 



455 




Fig. 227. — The power sprayer in use for spraying orchard trees. 



456 



Diseases of Economic Plants 




Fig. 228. — Power sprayer used in shade 
trees. 



Fig. 227. Smaller ma- 
chines differ essen- 
tially only in capacity. 

The adaptation of 
such outfits to various 
purposes is shown in 
Figs. 228, 229. 

The Spray Gun. — 
A recent development 
in power spraying is 
the spray gun. By 
its use one man can 



ing low plants, such as 
strawberries, potatoes, 
tomatoes, cabbage, 
etc. Several nozzles 
are attached and 
several rows can be 
treated at one time. 
Where a number of 
acres of truck crops are 
grown, this sprayer is 
of great advantage. 

Power sprayers. — 
For operating commer- 
cial orchards, power 
sprayers are a neces- 
sity, and are almost 
necessary for large 
home orchards, con- 
sisting, for example, 
of 50 or 60 large ap- 
ple trees. A modern 
power sprayer for use 
in large orchards is 
illustrated in Fig. 226, 
a still larger one in 




Fig. 229. — Power sprayer adapted to 
spraying beans. 



Fungicides 



457 



"^\ 



t\y^. 






^W' 












<*■ 


-^-u*. 


'^'i 


Mf 


'. 


--w^ 




■ 


^ 






Fig. 230. — The nozzles are turned at an angle to the rod so that the 
spray may be directed upward or downward. After Faurot. 



rapidly spray even the tallest fruit tree, a special device en- 
abling the operator to throw the spray to different distances. 
Spray guns are being used by many commercial growers. 

Conveyors. — To economize still further in time and labor, 
conveyors are used in many commercial orchards. These 
are 400-gallon tanks equipped with low-pressure, high-speed 
pumps, a.nd gasoline 
engines. The conveyor 
carries the spray from 
the mixing plant to 
the sprayer. Two hun- 
dred gallons of spray- 
ing material can be 
transferred from the 
tank of the conveyor 
to that of the sprayer 
in less than two min- 
utes. In this way the 
power sprayer is kept Fig. 231. — Spraying grapes. 




458 



Diseases of Economic Plants 



running almost continuously, thus sometimes doubling its 
output. 

The use of extension rods and the tower in spraying is 

shown in Fig. 230. 

Nozzles.^^^— The va- 
rious types of nozzles 
are illustrated in Fig. 
234. These include 
the Bordeaux type 
(upper left corner) , the 
Vermorel (lower left 



Fig. 232. — Spraying apparatus. 

corner), and the eddy-chamber type. 
The last is the best type of nozzle 
for spraying, and many forms of 
it are on the market. The eddy- 
chamber angle nozzle (lower right- 
hand corner) is a comparatively re- 
cent development. 






Fig. 234. — Various types of nozzles. 



Fig. 233. — Diagram of 
longitudinal section of 
a spray nozzle showing 
all the parts that may 
be found in the eddy- 
chamber nozzles. O, ori- 
fice; EC, eddy-chamber; 
P, post on the direct- 
ing disc, DD; C, Cap; 
W, washer; OB, oblique 
supply holes; S, strainer; 
R, reservoir; B, base of 
nozzle; D, disc, C, cen- 
tral supply hole. After 
Crane. 



Dusting machines. — These consist of various forms of 
blowers driven by hand or by gasoline engines. Fig. 235 
shows one of these machines in use for sulfuring. 



Fungicides 



459 



No matter what type of machine is in use, it is essential 
to keep on hand a supply of any parts that may be broken or 




Fig. 235. — Sulfuring machine in use. After Faurot. 

become worn out. The best companies are prompt in filling 
orders for repairs, but the grower cannot afford loss of even a 
very short time at critical periods. 



SOIL DISINFECTION 8-1^ 

Soil disinfection in the field has as yet in the main proved 
impracticable. All promising chemicals have been tried 
without avail. Electricity has not given beneficial results, 
and at present there is no hope of any practicable manner of 
ridding fields of parasites by any process of disinfection. In 
a few instances large applications of lime, formalin, or sulfur 
have proved beneficial (see sweet potato, onion, etc.), but 
the general practicability of such usage is doubtful. 

Disinfection of limited areas is, however, practicable, is 
largely employed, and has already resulted in great benefit, 
eliminating not only injurious fungi but insects and weeds as 
well. Cutting benches, flats, and other benches in the green- 
house, cold frames, and seed beds, and other small areas 
may be disinfected with advantage. The means to be em- 
ployed depend upon the area, its location, and the facilities at 
hand. The leading methods are given below: 

Baking. — Flats, pots, and other small containers of 
earth may often be satisfactorily disinfected by placing 
them upon a boiler or over a stove, or in an oven for a com- 
paratively long period. 

Permanent steam disinfectors. — A system of 13/2-inch 
pipes, which are perforated with 3^-inch holes on their under 
side at intervals of 6 inches throughout their entire length, 
may be placed about one foot below the surface of the soil. 
The pipes should run lengthwise of the bed, 18 inches apart, 
and be connected with a steam boiler. Before treatment the 
soil should be thoroughly spaded up and pulverized to permit 
ready access of the steam to all parts, and all fertilizers except 
commercial ones should be applied at this time, since fresh 
spores of the fungus are likely to be carried in if manure be 
added after disinfection. 

460 



Soil Disinfection 461 

The seed bed should be covered with several thicknesses of 
old burlap or blankets to confine the heat to the soil. The 
steam should be applied at a pressure of from 80 to 150 
pounds, since at high pressure the soil does not become so 
wet as when low-pressure steam is used. A treatment of from 
one to two hours is usually sufficient to disinfect thoroughly 
the soil to a depth of 18 inches. A few potatoes laid in the 
surfaces oil will indicate the thoroughness of the treatment 
by the degree to which they are cooked. The blankets may 
advantageously be left on for some time. 

While this method offers some advantages for seed beds 
of limited area, in that the pipes may be left in the ground 
and used year after year with little extra labor and may 
also be used for subirrigation, the initial cost of installa- 
tion, especially on large seed-bed areas, may be prohibitive. 

Inverted-pan method. — The method which has given 
the best results in practice, and which because of its simplic- 
ity and small cost recommends itself for use on large or 
small areas, is the invention of Mr. A. D. Shamel, of the 
U. S. Dept. Agr. Bur. of Plant Industry, and was devised 
by him to disinfect nematode-infested soils in Florida. The 
apparatus consists of a galvanized iron pan, 6' x 10' x 6" 
which is inverted over the soil and the steam admitted under 
pressure. The pan is supplied with steam-hose connections, 
has sharp edges, which are forced into the soil on all sides to 
prevent the escape of steam, and is fitted with handles for 
moving it from place to place, the weight of the entire pan 
being not over 400 pounds. 

The soil is prepared as in the greenhouse method, a few 
potatoes being buried at a depth of a foot to gauge the 
degree of heat attained, or a soil thermometer may be used if 
desired. The steam should be kept at as high pressure as 
possible, from 80 to 150 pounds being best, and the treatment 
should continue from 30 to 60 minutes, depending upon the 
pressure maintained and the character of the soil. Wet soils 
require more time than dry soils. In experiments conducted 
on tobacco seed beds in the spring of 1907, one hour's steam- 



462 



Diseases of Economic Plants 



ing at 80° C. gave best results in killing both the fungi and 
the weed seeds. When one section of the bed is treated, the 
pan is lifted and carried to another portion, and the operation 
repeated until the entire bed is steamed. 




Fig. 236. — Disinfecting with steam by the inverted-pan method. 
After Johnson. 



The inverted-pan method is particularly applicable in 
disinfecting greenhouse benches or flats. Streaming steam 
from the heating system passed into the pan for one and one- 
half hours suffices. A steam hose connecting the pan with a 
traction engine makes a serviceable out-of-door outfit. 

The Sargent method. — Disinfection by a system of 
steam pipes arranged in the form of a harrow, with hollow. 



Soil Disinfection 



463 



perforated teeth, has proved satisfactory under some condi- 
tions. 

Surface firing. — Surface firing of seed beds has been a 
common practice for years in some tobacco sections, par- 
ticularly in Kentucky and other southern states, the end in 
view being the improvement of the tilth of the soil and the 
killing of weed seeds rather than the destruction of any 
fungous disease. In Italy burning is now considered a part 




Fig. 237. — Disinfecting soil with a Sargent disinfeetor. Original. 

of the regular method of tobacco seed-bed preparation, it 
having been resorted to as a preventive of root-rot due to 
Thielavia. 

Two methods of surface firing are in vogue; the first, 
by direct firing, the second requiring the use of a pan. In 
the direct method, the land to be disinfected is first thor- 
oughly pulverized and manure applied. It is then covered 
with straw, brush, and wood sufficient to make a hot fire. 
This is ignited and allowed to burn an hour or so, after 
which the ashes are raked into the surface soil. 

The second method, pan firing, consists in the use of a 
sheet-iron pan, 3' by 9', which is set in the middle of the seed 



464 Diseases of Economic Plants 

bed and a fire built under it. The soil on one side of the pan 
to a depth of 6 inches is shoveled and heated, great care being 
taken to keep it moist, otherwise the humus would be burned 
out and the physical texture seriously altered. After an 
hour this soil is put back and that from the other side of the 
pan subjected to the same treatment, and then the pan 
moved along to a new place. The soil underneath the pan 
itself is thereby subjected to heat for two hours. 

Disinfection by formalin. — The use of formalin for the 
disinfection of greenhouse soil and of tobacco seed beds 
against Corticium has been in vogue for some time with 
excellent results. It furnishes a very simple means of disin- 
fection as follows: The beds are thoroughly prepared as for 
the other methods of disinfection described and are then 
drenched with a 2 per cent formalin solution using two 
quarts of this solution to the square foot of bed space. The 
solution should be put on with a watering pot with a rose 
orifice and distributed as evenly as possible over the bed, so 
as to wet the soil thoroughly to the depth of a foot. It will, 
in most cases, be necessary to put this solution on in two or 
three applications, as the soil will not immediately take 
in this quantity of water. The beds should then be covered 
with heavy burlap or a tarpaulin to retain the fumes for a day 
or so, and then aired for a week before sowing the seed. 

Spring applications of formalin are open to the following 
objections: The addition of such a large quantity of water 
to the soil keeps it wet and cold longer than would naturally 
be the case, thus delaying germination as well as subsequent 
growth; the necessity of airing the beds to remove the for- 
malin fumes and to allow the soil to dry out also causes delay 
in seeding. To obviate these difficulties the beds should be 
treated in the fall, before freezing. 

Disinfection by sulfuric acid. — One-eighth to three- 
sixteenths fluid ounce of commercial sulfuric acid in from one 
to two pints of water, according to the humidity of the soil, is 
applied per square foot of soil immediately after the seeds are 
covered. This treatment is used principally for conifers. 



Soil Disinfection 465 

Abundant watering is necessary to prevent root injury of the 
seedlings. 

Disinfection by copper-sulfate. — This chemical may be 
used up to one-fourth ounce per square foot. It is employed 
chiefly for conifer seed beds. 

Disinfection by zinc-chlorid. — Five-eighths of an ounce 
of this solution per square foot may be employed for conifer 
seed beds, but it is more expensive than copper-sulfate. 

Disinfection by hot water. ^^^ Pots, flats, etc., may be 
disinfected by submersion in hot water, 98° C. (208° F.) for 
five minutes. The quantity of water necessary increases 
with the volume of soil to be treated ; thus for 8" pots about 
3000 cc. of water is needed at 98° C. or 2000 cc. of boiling 
water. On shallow benches boiling water should be used at 
the rate of 7 gallons per cubic foot of soil. 



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Apple tree anthracnose. Ore. Agr. Exp. Sta. Bui. 60. 1900. 
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INDEX 



Abutilon, 407. 

Acal.vpha, 407. 

Acanthorhynchus vaccinii, 111. 
Acanthostigma, 379. 
Achillea, 407. 
Acremonium, 191. 
Actinomyces scabies, 163, 220. 
Actinonema, 430. 
Adonis, 407. 
iEcidium, 119, 390, 411, 423. 

gossypii, 350. 
Agave, 408. 
Ageratuni, 407. 
Agropyron, 277, 278, 340. 
Agrostis, 277, 278, 340. 
Aira, 278. 
Albugo, 173, 408. 

bliti, 164. 

Candida, 172, 196, 427. 

ipomoejB-panduranai, 250, 427. 

tragopogonis, 241. 
Alder, 361, 367, 369, 371, 379, 

381. 
Alfalfa, 22, 23, 24, 88, 163, 321. 
Algal leaf-spot, 144, 147. 
Allseed, 163. 
Almond, 25, 74, 87. 
Alopecurus, 277, 278. 
Alternaria, 57, 69, 195, 217, 328, 
352, 415, 427. 

brassicae, 169. 

var. nigrescens, 183. 

citri, 141. 

dianthi, 415. 

panax, 193. 

solani, 226, 264. 

violse, 436. 
Alyssum, 407. 
Amarantus, 407, 408. 
Amerosporium oeconomicum, 335. 
Ammoniacal copper carbonate, 
447. 



Ampelopsis, 439. 
Andromeda, 409. 
Anemone, 407, 409. 
Angular loaf-spot, 114, 185, 

337, 349, 424. 
AnthostomelLa, 145. 
Anthoxanthum, 277, 278. 
Anthracnose, 102, 112, 115, 
128, 135, 143, 147, 151, 
173, 180, 192, 194, 199, 
241, 242, 264, 280, 300, 
309, 317, 324, 328, 330, 
339, 340, 342, 345, 383, 
392, 395, 408, 409, 412, 
424, 428, 420, 430, 433, 
435, 437. 
Antirrhinum, 407. 
Aposphseria, 134. 
Apple, 23, 31, 87, 361, 367, 

369, 372. 
Apricot, 74, 87, 90. 
Aquilegia, 407. 
Aralia, 408. 

Arbor- vitae, 367, 369, 371, 380. 
Arbutus, 88. 
Armillaria, 117, 367. 
mellea, 53, 370. 
root-rot, 79, 96, 101. 
Arrenantherum, 277. 
Arsenical injury, 240. 
Artichoke, 435. 

Ascochyta, 134, 210, 369, 379. 
abelmoschi, 201. 
armoraciae, 195. 
ehrysanthemi, 419. 
clematidina, 420. 
leaf-spot, 327. 
medicaginis, 327. 
primulae, 429. 
Ash, 23, 364, 367, 368, 369, 

380, 381. 
Asparagus, 10, 25, 149, 407. 



257, 



119, 
152, 
217, 
307, 
331, 
388, 
421, 
434, 



368, 



379, 



491 



492 



Index 



Aspen, 359, 367. 
Aspidistra, 409. 
Aster, 22. 

china, 409. 
Asterina, 379. 
Aueuba, 407. 
Avena, 277, 278. 
Avocado, 135. 
Azalea, 113, 411. 

Bacillus, 427. 

amylovorus, 41, 62, 70, 74, 79, 
101. 

carotovorus, 172, 173, 178, 208, 
412, 420. 

coli, 144. 

lathy ri, 435. 

melonis, 188. 

phytophthorus, 231. 

sorghi, 307. 

tracheiphilus, 182. 
Bacteria, 217, 299, 304, 342, 369, 

389, 426. 
Bacterial blight, 213, 337. 

leaf -spot, 164, 422. 

rot, 199. 

spotting, 200, 416. 

wilt, 260. 
Bacterium michiganense, 260. 

mori, 393. 

rathayi, 339. 

teutlium, 164. 
Balm, 411. 
Balsam, 367. 
Bamboo, 411. 
Banana, 135. 
Barberry, 312, 411. 
Bark canker, 56, 69. 

disease, 386. 
Barley, 163, 280. 
Barnyard-grass, 338. 
Barrel pump, 454. 
Bartonia, 407. 
Basswood, 372. 
Bean, 22, 23, 25, 152, 163. 
Beckmannia, 277. 
Bed-rot, 257. 
Beech, 359, 361, 364, 365, 367, 369, 

380, 381. 
Beet, 22, 23, 25, 27, 87, 159, 163. 
Begonia, 24, 407, 408, 412. 



Bellflower, 23. 

Berberis, 407. 

Bermuda lily disease, 426. 

Birch, 359, 361, 364, 365, 367, 368, 
369, 371, 379, 380, 381, 382. 

Bitter-pit, 54. 

Bitter-rot, 31, 69, 72, 132. 

Blackberry, 87, 102. 

Black-chaff, 319. 

Black-heart, 148, 235. 

Black-knot, 75, 97. 

Blackleg, 169, 231. 

Black-mold, 57, 69, 169, 196, 210, 
213, 216, 243, 328, 331, 427. 

Black-root, 163, 173. 

Black-rot, 42, 47, 72, 120, 141, 165, 
194, 247, 260. 

Black-rot canker, 69. 

Black-rust, 350. 

Black-scurf, 225. 

Black-smut, 146, 302. 

Black-spot, 70, 74, 79, 90, 101, 205, 
217. 
canker, 430. 

Black-stem-rust, 282, 298, 305, 310, 
339, 340. 

Black-walnut, 359. 

Blast, 110, 339, 380. 

Bletia, 412. 

Blight, 62, 70, 74, 79, 101, 144, 155, 
165, 193, 195, 199, 203, 242, 
251, 260, 282, 294, 299, 307, 
324, 389, 393, 394, 403, 404, 421, 
422, 425, 427. (See also early- 
blight, southern-blight, late- 
blight, blister-blight, blossom- 
blight, brown- blight, bacter- 
ial-blight, body-blight, pod- 
blight, stem-blight, coryneum- 
blight, leaf-blight, cane-blight.) 

Blister-cankei, 44. 

BHster-rust, 119, 395. 

Blossom-blight, 41. 

Blossom-drop, 265. 

Blossom-end rot, 263. 

Blossom rot, 191. 

Blotch, 37. 

Blueberry, 110. 

Bluegrass, 280, 338. 

Blue-mold, 51, 108, 132, 141, 193, 
250. 



Index 



493 



Blue-stem, 110. 
Bluing, 397. 
Body-blight, 41. 
Boll-rot, 346. 
Bordeaux-injury, 450. 
Bordeaux mixture, 6, 440. 
Botryosphaeria, 346. 

berengeriana, 395. 

marconii, 353. 

ribis, 113. 
Botrytis, 10, 20, 174, 369, 416, 421, 
422, 426, 427, 428, 430, 436. 

allii, 206. 

blight, 195. 

cinerea, 198. 

fascicularis, 192. 

rot, 134. 
Box-elder, 369. 
Breeding for resistance, 7. 
Bremia lactucEe, 198. 
Broccoli, 165. 
Bromus, 277, 278. 
Bronzing, 433. 
Broom corn, 283. 
Broom rape, 331. 
Brown-canker, 432. 
Brown-checked wood-rot, 361. 
Brown leaf-rust, .305. 
Brown leaf-spot, 395. 
Brown-rot, 55, 69, 73, 74, 75, 79, 

101, 135. 
Brown-spot, 292. 
Brunnissure, 131. 
Brussels-sprouts, 163, 165. 
Bucket pumps, 452. 
Buckeye, 390. 
Buckeye-rot, 265. 
Buckwheat, 22, 165. 
Bud-rot, 144, 417. 
Bunt, 314. 

Burgundy mixture, 448. 
Butternut, 359, 361, 367, 380, 381, 
382. 

Cabbage, 22, 23, 26, 163, 165. 

Cacao, 135. 

Cacao-disease, 245. 

Calamagrostis, 277, 278. 

Calendula, 407. 

California vine-disease, 131. 

Calla, 412. 



Callistephus, 407, 409. 
Calospora vanillse, 148. 
Camellia, 408, 413. 
Campanula, 407, 408. 
Candytuft, 168. 
Cane-blight, 105, 113. 
Canker, 32, 35, 42, 69, 72, 135, 137, 
146, 251, 368, 385, 390, 401, 
402, 405, 423, 432. (See also 
Pacific coast canker, blister- 
canker, black-rot canker, brown 
canker.) 
Canna, 413. 
Cantaloupe, 173. 
Caper, 173. 

Capnodium, 144, 408, 413. 
Carnation, 22, 87, 414. 
Carrot, 22, 23, 25, 173. 
Cassandra calyculata, 113. 
Castor-bean, 174. 
Catalpa, 25, 368, 373, 379, 380, 

381, 382. 
Cauliflower, 23, 163, 165. 
Cedar, 69, 367, 383. 
Celery, 22, 25, 163, 174. 
Celosia, 407. 
Cenangium, 369. 
Centaurea, 407. 
Cephaleuros, 25 1 . 

virescens, 144, 147. 
Cephalothecium, 395. 

roseum, 49. 
Ceratostomella pilifera, 397. 
Cercospora, 201, 217, 348, 379, 
439, 524. 

althaeina, 424. 

angulata, 114. 

apii, 176. 

armoraciae, 196. 

beticola, 159, 244. 

boUeana, 146. 

capsici, 217. 

circumscissa, 96. 

cofTeicola, 145. 

concors, 234. 

cruenta, 159, 337. 

fusca, 395. 

leaf-spot, 132, 159, 191, 327, 
331. 

longipes, 245. 

medicaginis, 327. 

microsora, 391. 



494 



Index 



nicotianse, 257. 

personata, 214. 

phlogina, 429. 

resedse, 426. 

richardisecola, 413. 

rosseicola, 433. 

shot-hole, 96. 
Cercosporella albomaculans, 173. 

persica, 96. 
Cereal, 266. 

anthracnose, 266. 

nists, 275. 

smuts, 266. 

special diseases, 280. 
Chamaecyparis, 368, 369. 
Charcoal-rot, 251. 
Chard, 159. 
Charrina, 132. 
Cherry, 22, 25, 75, 87, 90, 96, 97, 

361, 367, 369. 
Chestnut, 11, 87, 361, 367, 368, 
369, 371, 373, 380, 381, 386, 
388. 
China-berry, 23, 369, 372. 
Chive, 201. 

Chlorosis, 148, 265, 295. 
Choanephora cucurbitaruni, 191. 
Chrysanthemum, 23, 88, 407, 408, 

418. 
Chrysophlyctis, 224. 
Cineraria, 24, 407, 420. 
Citrus fruits, 135. 
Citrus knot, 144. 
Cladosporium carpophilum, 82, 99. 

citri, 142. 

cucumerinum, 187. 

fulviim, 262. 

herbarum, 140, 439. 

macrocarpum, 243. 

viticolum, 132. 
Claviceps paspali, 340. 

purpurea, 304. 

rolfsii, 340. 
Cleistothecopsis circinans, 205. 
Clematis, 24, 407, 420. 
Clethra alnifolia, 113. 
Clitocybe, 52, 372. 

root-rot, 96. 
Clover, 22, 24, 88, 163, 328. 
Club-root, 26, 168, 
Cluster-cup, 117, 119, 350, 409. 



Coccomyces, 75. 

prunophorse, 98. 
Cocoanut, 144. 
Coffee, 144. 
Coleosporium ipomceae, 251, 427. 

senecionis, 420. 

solidaginis, 401, 410. 
Coleus, 24, 407. 
Collard, 165. 

Colletotrichum, 20, 145, 148, 151, 
192, 205, 244, 251, 345, 352, 
379, 427, 428. 

agaves, 408. 

antirrhini, 434. 

bletiae, 412. 

carica, 145. 

cereale, 280, 300, 307, 317. 

erumpens, 241. 

falcatum, 309. 

gloeosporioides, 135, 143, 147. 

higginsianum, 173. 

lagenarium, 180. 

lindemuthianum, 152. 

malvarum, 424. 

nigrum, 217. 

omnivorum, 409. 

phomoides, 264. 

primulse, 429. 

spinaceae, 242. 

trifqlii, 324, 330. 

violse-tricoloris, 437. 
CoUybia, 367. 
Colocasia, 420. 

Combined fungicide and insecti- 
cide, 449. 
Common-scab, 220. 
Completoria complens, 422. 
Compressed air sprayers, 453. 
Conifers, 355, 358, 361, 367, 368, 

369, 371, 376, 379, 380. 
Coniothyrium, 105, 395. 

fuckelii, 44. 
Conveyors, 457. 
Copper-blight, 251. 
Copper sulfate, 448. 
Copper-sulfate treatment, 271. 
Coreopsis, 407. 
Core-rot, 57. 
Corn, 22, 88, 163, 283. 
Cornus, 408. 
Corrosive sublimate, 449. 



Index 



495 



Corticium, 20, 135, 144, 146, 163, 
193, 194, 376, 402, 407, 410, 
435, 439. 

koleroga, 145. 

stevensii, 47. 

vagum, 21, 157, 162, 165, 198, 
213, 225, 257, 265, 349, 417. 
Coryneum beijerinekii, 87. 
Coryneum-blight, 74, 87. 
Cosmos, 407, 421. 
Cotton, 22, 23, 24, 88. 
Cottonwood, 367, 369, 372, 380, 401. 
Cottony-rot, 137. 
Covered smut, 282, 297. 
Cowpea, 23, 24, 26, 331. 
Crab-grass, 339. 
Cranberry, 110. 
Cress, 163. 
Cronartium, 369. 

cerebrum, 400. 

ribicola, 116, 395. 
Crown-gall, 51, 69, 73, 74, 79, 87, 
101, 104, 132, 164, 350, 405, 
408, 422, 433. 
Crown-rot, 144, 241. 
Crown-rust, 298, 339. 
Crown-wart, 325. 
Crucifers, 24, 165. 
Cryptosporella, 369. 

anomala, 389. 

viticola, 129. 
Cucumber, 22, 25, 26, 178. 
Cucurbit spraying, 191. 
Cucurbits, 24, 178. 
Cuphea, 407. 
Cupressus, 369. 
Curing-house disease, 259. 
Curl, 77, 84. 
Curly-dwarf, 233. 
Curly-top, 160. 
Currant, 22, 113, 367. ' 
Cuscuta, 325. 

epilinum, 352. 
Cutting-bench disease, 407. 
Cuttings, 19. 
Cyanospora, 369. 
Cyclamen, 408, 421. 
Cycloconium oleaginum, 147. 
Cylindrocladium scoparium 432. 
Cylindrosporium, 75, 98, 379. 

chrysanthemi, 420. 



clematidis, 420. 

humuli, 195. 
Cypress, 367. 
Cystospora batatae, 249. 
Cytospora, 78, 86, 369, 405, 423. 

chrysosperma, 401. 

Dactylis, 277, 278, 339. 

Dajdalea, 367. 

Dahlia, 24, 407, 408, 421. 

Daisy, 408, 422. 

Damage caused by plant diseases, 

10. 
Damping off, 19, 24, 163, 173, 178, 
193, 194, 198, 213, 252, 258, 
265, 303, 328, 349, 352, 376, 
399, 427. 
Dandelion, 163. 
Daphne, 23. 
Dasyscypha, . 369. 

resinaria, 390. 
Dead-arm, 129. 
Decay in live trees, 354. 
Decay of dead parts, 373. 
Deciduous trees, 364, 365, 367, 368, 

371, 374. 
Dendrophoma, 353. 
Dewberr3^ 88, 102. 
Dianthus, 407, 408. 
Diaporthe, 369. 

batatatis, 250. 

phaseolorum, 158. 

umbrina, 432. 
Dibotryon morbosum, 75, 97. 
Didymellina viridis, 425. 
Didymosphseria, 379. 
Dieback, 74, 78, 86, 135, 144, 395, 
402, 404. 

canker, 57, 69. 
Diplocarpon rosae, 430. 
Diplodia, 135, 144, 148, 187, 402, 
420. 

cacaoicola, 245. 

gossypina, 346. 

longispora, 394. 

macrospora, 287. 

tubericola, 250. 

zeae, 287. 
Diplodina, 190. 
Diseases due to impure air, 26. 
Disease prevention, 236. 



493 



Index 



Disinfection of seeds, 7. 

Doassansia gossypii, 349. 

Dodder, 144, 325, 331, 352. 

Dogwood, 369, 381. 

Dothichiza, 369. 
populea, 401. 

Dothidea, 369. 

Dothidella, 394. 

Dothiorella gregaria, 404. 

Double-blossom, 108. 

Downy-mildew, 125, 158, 164, 171, 
178, 196, 198, 203, 244, 263, 
295, 327, 338, 433, 437. 

Dracaena, 422. 

Dracocephalum, 408. 

Drop, 26, 27, 158, 164, 170, 174, 
193, 196, 258, 409, 426, 435. 

Drupes, 74, 368. 

Dry-rot, 230, 250, 287, 289, 374. 

Dusting machines, 458. 

Dwarf leaf-rust, 282. 

Early-blight, 176, 226, 204. 
Ear-rots, 286. 
Echinodontium, 367. 

tinctorum, 389. 
Eel-worms, 320, 412. (See also 

nematodes.) 
Egg plant, 22, 23, 25, 26, 192. 
Einkorn, 310. 
Elder, 381. 
Elm, 23, 25, 359, 364, 367, 369, 379, 

380, 381, 388. 
Elymus, 277, 278. 
Emmer, 310. 
Endomyces, 57. 
Endothia, 369. 

parasitica, 386. 
End-rot, 112. 

Entomosporium, 68, 70, 379. 
Entyloma ellisii, 242. 
Ergot, 282, 300, 304, 320, 339, 340. 
Erigeron, 408. 
Eriobotrya, 407. 
Erysimum, 407. 
Erysiphe, 173, 242, 338. 

cichoracearum, 420, 429, 436. 

communis, 421. 

graminis, 317. 

polygoni, 159, 165, 187, 213, 337. 
Eupatorium, 408. 



Euphorbia, 328, 407. 
European canker, 55, 72, 401. 

rust, 116. 
Evonymus, 408. 
Exoascus deformans, 84. 
Exobasidium, 110, 251, 409, 411. 

oxycocci, 112. 
Extension rod, 458. 

Fabrsea maculata, 68, 70. 

mespili, 73. 
Falcata, 155. 
Favolus, 367. 
Ferns, 422. 
Festuca, 277, 278. 
Fiber-plant, 23, 343. 
Field crops, 149. 
Field sprayers, 454. 
Fig, 23, 25, 145. 
Filbert, 369, 389. 
Fir, 365, 367, 368, 369, 371, 373, 

380. 
Fire-blight, 41, 62, 74. 
Fistulina, 367. 
Flag-smut, 316. 
Flax, 23, 24, 26, 350. 
Flower-blight, 379. 
Flowering almond, 408. 
Flowers of sulfur, 449. 
Flyspeck, 56, 69. 
Fomes, 367, 402. 

annosus, 53, 371. 

applanatus, 365. 

everhartii, 364. 

fomentarius, 364. 

fraxinophilus, 381. 

fulvus, 361. 

igniarius, 359. 

juniperinus, 383. 

pinicola, 365, 401. 

ribis, 117, 402. 

rimosus, 391. 
Foot-rot, 316. 
Forage crops, 321. 
Formalin, 449. 
Formalin dry method, 270. 
Formalin long-time treatment, 271. 
Formalin wet method, 270. 
Foxtail, 163. 
Frost injury, 54. 
Frosty-mildew, 96, 348. 



Index 



497 



Fruit-rot, 57, 134, 145, 217, 263. 
Fruit-spot, 57, 187. 
Fumago vagans, 57, 265. 
Fungicides, 440. 

Fusarium, 20, 146, 178, 213, 249, 
257, 289, 318, 325, 331, 346, 
376, 399, 416, 418, 420, 435. 

boll-rot, 346. 

conglutinans, 172, 409. 

lini, 350. 

lycopersici, 250. 

malli, 210. 

oxysporum, 228. 

rubi, 108. 

vasinfectum, 181, 193, 201, 331, 
343. 

violae, 437. 
Fusicladium, 35, 68, 379, 402. 

dendriticum, 147. 

efifusum, 394. 
Fusicoccum, 129. 

putrefaciens, 112. 

Gall, 24, 113, 368, 402, 409, 420, 
427. (See also crown-gall, 
nematode.) 
Garlic, 201. 

Gaultheria procumbens, 113. 
Gaylussacia resinosa, 113. 
General diseases, 19, 354. 
Geranium, 422. 
Gibbera, 110. 

Gibberella saubinetii, 318, 331. 
Ginseng, 24, 193. 
Gladiolus, 423. 
Gloeodes pomigena, 55. 
Gloeosporium, 20, 31, 44, 72, 102, 
115, 145, 148, 217, 380, 395, 
403, 430, 435. 

ampelophagum, 128. 

apocryptum, 392. . 

caulivorum, 331. 

euphorbiae, 435. 

medicaginis, 328. 

melongenae, 192. 

musarum, 135. 

rosae, 433. 

\dolse, 437. 
Glomerella cingulata, 31, 72, 112, 
395, 421, 430, 435. 



gossypii, 345. 

piperata, 217. 

psidii, 146. 
Glume blotch, 319. 
Gnomonia, 380. 

leptostyla, 382, 403. 

ulmea, 388. 

veneta, 403. 
Gnomoniella, 380. 
Godetia, 407. 
Golden glow, 407. 
Goldenseal, 24, 195. 
Gooseberry, 10, 117, 367. 
Granville wilt, 253. 
Grape, 25, 87, 120. 
Graphiola-blight, 428. 
Graphiola phcenicis, 428. 
Grass, 23. 163, 338. 
Gray-blight, 251. 
Gray-mold, 108, 174, 192, 198, 416, 

422, 426, 430, 436. 
Gray-rot, 132. 
Green-smut, 301. 
Guava, 146. 
Guignardia, 110. 

aesculi, 390. 

bidwellii, 120, 439. 

vaccinii, 110. 
Gummosis, 74, 141. 
Gymnoconia interstitialis, 104. 
Gymnosporangium, 39, 67, 369, 376, 
383, 423. 

clavipes, 69. 
Gypsophila, 407. 

Hackberry, 379, 380, 381. 
Hairy-root, 26, 87, 162. 
Halo-blight, 299. 
Hard-rot, 423. 
Hawthorn, 379, 407, 423. 
Hazel, 369, 380, 389. 
Head-smut, 286, 309. 
Heart-rot, 361, 364, 389, 402. 
Hedera. 425. 
Helianthus, 407. 

Helicosporium nymphsearum, 439. 
Helminthosporium, 282, 317, 402. 

carpophilum, 95. 

inconspicuum, 294, 300. 

teres, 283. 



498 



Index 



Hemileia vastatrix, 144. 

Hemlock, 365, 367, 368, 369, 371, 

373, 379, 380. 
Hemlock, western, 389. 
Hemp, 163, 353. 
Hendersonia, 145, 380. 
Hepatica, 96, 423. 
Herpotrichia, 380. 
Heterosporium, 425. 

echinulatum, 416. 

variable, 243. 
Hibiscus, 23, 407, 423. 

sabdariffa, 241. 
Hickory, 359, 367, 380, 381. 
Historical, 1. 

concerning prevention, 3. 

important events, 8. 
Holcus, 277, 278. 
Hollow-heart, 235. 
Hollow-stem, 265. 
Hollyhock, 10, 24, 423. 
Honey-locust, 381. 
Honeysuckle, 88, 407, 408. 
Hop, 87, 163, 195. 
Hordeum, 277, 278. 
Hornbeam, 359, 381. 
Horse-chestnut, 364, 367, 368, 369, 

380, 381, 390. 
Horse-radish, 195. 
Hot-water treatment, 271, 274. 
Huckleberry, 110, 113. 
Hydnum, 367. 

erinaceus, 361. 
Hydrangea, 23, 425. 
Hydrastis, 195. 
Hymenochsete, 402. 
Hypertrophy, 112. 
Hypochnose, 47, 69, 73. 
Hypoderma, 380, 397. 
Hystrix, 277. 

Iberis, 407, 

Illosporium, 47. 

Impatiens, 407. 

Incense cedar, 369, 380. 

Inga, 380. 

Injury to seed by treatment, 277. 

Insecticide, 449. 

Internal brown-spot, 236. 

Inverted-pan method, 461. 

Irpex, 67, 402. 



Isariopsis griseola, 159. 
Ivy, 425. 

Japan clover, 337. 

Java black-rot, 420. 

Java drv-rot, 250. 

Jelly end-rot, 230. 

Jerusalem artichoke, 435. 

Johnson grass, 339. 

Jonathan-spot, 54. 

Juniper, 367, 368, 369, 380, 381. 

Juniperus, 40, 69, 383. 

Kafir, 307. 
Kale, 163, 165. 
Kalmia angustifolia, 113. 
Keithia, 380. 
Kernel-smut, 283, 308. 
Kernel-spot, 395. 
Knapsack sprayer, 454. 
Knot, 147, 427. (See also root-knot.) 
Kochia, 407. 
Koeleria, 277, 278. 
Kohl-rabi, 163, 165. 
Kuehneola albida, 105. 
gossypii, 349. 

Labrella pomi, 56. 

Lsestadia, 251. 

Larch, 367, 368, 369, 371, 373, 

380, 390. 
Large leaf-spot, 388. 
Larkspur, 407, 426. 
Lasiodiplodia triflorge, 99. 
Late-blight, 174, 217, 263. 
Late-rust, 105. 
Lathryus, 407. 
Laurel, 425. 
Lavatera, 407. 
Leaf-anthracnose, 194. 
Leaf-blight, 68, 70, 134, 183. 187, 

195, 244, 250, 348, 398, 402, 

425. 
Leaf-blotch, 159, 234, 390. 
Leaf-cast, 397. 
Leaf-curl, 233, 394. 
Leaf-glaze, 191. 
Leaf-mold, 262, 416. 
Leaf -perforation, 199. 
Leaf-roll, 233, 265. 
Leaf-rot, 145. 
Leaf-scorch, 164. 



Index 



499 



Leaf-spot, 47, 68, 75, 98, 104, 114, 
119, 134, 135, 144, 145, 146, 
147, 159, 165, 173, 176, 178, 
185, 190, 191, 192, 195, 196, 
201, 214, 217, 241, 243, 244, 
245, 251, 257, 262, 295, 298, 
321, 331, 335, 338, 339, 379, 
382, 388, 391, 392, 405, 411, 
413, 415, 418, 420, 421, 422, 
424, 425, 426, 427, 428, 429, 
433, 434, 435, 439. 

Leak, 134, 234, 264. 

Leather-leaf, 113. 

Legumes, 23, 24, 321. 

Lentil, 163. 

Lentinus, 367. 

Lenzites, 367. 

Leopard-spot, 152, 

Leptospharia coniothyrium, 105. 
leaf-blight, 319. 
saeehari, 245. 
tritici, 319. 

Leptostroma, 380. 

Leptothyrium pomi, 380. 

Lespedeza, 337. 

Lettuce, 25, 27, 88, 196. 

Libertella, 146. 

Libocedrus, 369. 

Lichens, 144. 

Ligu strum, 407. 

Lilac, 426. 

Lily, 426. 

Lily-of-the-valley, 426. 

Limb-blight, 146. 

Lime, 23. 

Lime-sulfur, 443. 

Lime-sulfur injury, 451. 

Lime-sulfur wash, 445. 

Linaria, 407. 

Linden, 23, 364, 368, 369, 379, 380, 
381, 391. 

Linum, 407. 

Little-peach, 95. 

Lobelia, 407. 

Locust, 23. 361, 367, 368, 371, 379, 
380, 381, 391. 

Lolium, 277, 278. 

Lonicera, 408. 

Loose-smut, 280, 296, 315. 

Lophodermium, 380. 
brachysporum, 398. 



Loquat, 147. 
Lupine, 163. 
Lychnis, 407. 
Lythrum, 407. 

Macrophoma, 113, 146. 

tumefaciens, 402. 
Macrosporium, 216, 304, 380. 

herculeum, 196. 

leaf-spot, 173. 

parasiticum, 210. 

porri, 210. 

sarcinaeforme, 331. 
Magnolia, 369, 379. 
Malnutrition, 173. 
Mangels, 159. 
Mango, 147. 
Mangold, 159. 

Maple, 23, 359, 361, 364, 365, 367, 
368, 369, 371, 379, 380, 381, 
392. 
Marasmius, 251. 

saeehari, 245. 
Marigold, 88. 
Marssonina, 380, 382, 403, 405. 

ochroleuca, 388. 

panattoniana, 199. 

populi, 402. 
Matthiola, 407. 
Medlar, 73. 
Melampsora, 401. 

lini, 352. 

saliciscaprae, 405. 
Melampsorella elatina, 390. 
Melampsoridium betulinae, 382. 
Melanose, 144. 
Melaxuma, 404. 
Melon, 178. 

Merulius lacrymans, 374. 
Mesquite, 372. 
Microsphsera, 394. 

alni, 394, 426, 435. 

diffusa, 337. 

euphorbiae, 241. 
Mierostroma, 380. 

juglandis, 395. 
Mignonette, 426. 
Migration of diseases, 10. 
Mildew. (See downy mildew, pow- 
dery-mildew.) 
Millet, 295. 



500 



Index 



Milo, 307. 

Mistletoe, 144, 375, 390, 395. 
Modified hot-water treatment, 272. 
Mold, 75, 200, 427, 428, 439. (See 
also gray-mold, sooty-mold, 
black-mold, blue-mold.) 
Monilia, 55, 75, 79, 101. 
Monilochsetes infuscans, 250. 
Monochetia, 380. 

desmazierii, 388. 
Moon-flower, 427. 
Morning-glory, 23, 427. 
Mosaic, 159, 186, 217, 233, 258, 265, 

350, 435. 
Mountain-ash, 368, 369, 380, 381. 
Mountain -laurel, 425. 
Mulberry, 23, 25, 367, 368, 369, 

372, 381, 393. 
Mushroom, 200. 
Muskmelon, 23, 25, 26, 178. 
Mustard, 163. 
Mycogone perniciosa, 200. 
Mycosphaerella, 135, 173, 338. 

citruUina, 190. 

fragariae, 132. 

gossypina, 348. 

grossulariae, 114. 

leaf-spot, 114. 

pinodes, 210. 

rosigena, 433. 

rubina, 107. 

sentina, 68. 
Myxosporium, 56, 369. 

Nasturtium, 427. 

Necator decretus, 145. 

Neck-rot, 206. 

Necrosis, 129. 

Nectarines, 90. 

Nectria, 135, 148, 251, 369, 402. 
galligena, 55, 72. 
ipomoeae, 192. 

Nematode, 24, 26, 146, 159, 162, 
169, 191, 193, 195, 200, 213, 
217, 251, 259, 265, 320, 348, 
421, 435. 

Neocosmospora, 214. 

Neofabrea malicorticis. 44. 

Neopeckia, 380. 

Net-blotch, 283. 

Net-necrosis, 236. 

Nozzles, 458. 



Nummularia, 369. 

discreta, 44. 
Nursery-blight, 395. 
Nursery stock, 23. 
Nut-trees, 89. 

Oak, 359, 361, 362, 364, 365, 367. 
368, 369, 371, 372, 379, 380, 
381, 394. 
Oat, 163, 280, 296. 
CEdema, 265. 
Oidium, 50, 122, 241, 420, 435, 436. 

citri-aurantu, 144. 

mespilinum, 73. 
Okra, 25, 201. 
Oleander, 88, 369, 408, 427. 
Olive, 147, 367, 369. 
Olpitrichum, 346. 
Onion, 25, 26, 201. 
Orange, 367, 368, 369. 
Orange leaf-rust, 312. 
Orange-rust, 104. 
Orchard grass, 280, 339. 
Orchard trees, 371. 
Orchids, 427. 
Ornamental plants, 406, 
Orobanche, 159, 259. 

minor, 331. 
Osage orange, 380, 394. 
Ozonium, 146, 201, 248, 323. 

omnivorum, 23, 53, 346, 372. 

root-rot, 372. 

Pacific coast canker, 44. 

Pseonia, 407. 

Pale-rot, 73. 

Pale-spot, 173. 

Palm, 408, 428. 

Palmetto, 368. 

Panicularia, 277. 

Panicum, 338. 

Pansy, 436. 

Parsley, 174. 

Parsnip, 88, 163, 174. 

Paspalum, 340. 

Patellina, 134. 

Pea, 22, 24, 25, 163, 210. 

Peach, 25, 79, 87, 90, 367, 369. 

Peacock leaf -spot, 193. 

Peanut, 23, 214. 

Pear, 62, 361, 364, 368, 369, 372. 



Index 



501 



Pecan, 25, 88, 369, 379, 380. 381, 394. 
Pecky heart-rot, 35S. 
Pecky-rot, 384. 
Pelargonium, 407, 422, 
Penicillium, 26, 108, 148, 193. 

(ligitatum, 141. 

expansum, 51, 250. 

italicum, 141. 
Pentstemon, 408. 
Peony, 24, 88, 428. 
Pepper, 23, 25, 215. 
Perforation, 405. 
Peridermium, 376, 380, 400, 401. 
Peronoplasmopara cubeasis, 178. 
Peronospora, 164, 196, 295. 

effusa, 244. 

parasitica, 171. 

schleideni, 203. 

sparsa, 433. 

trifoliorum, 327. 

vicia?, 338. 

violae, 437. 
Persimmon, 23. 
Pestalozzia, 251, 380, 402. 

funerea, 194. 

guepini, 413. 
Petunia, 407, 429. 
Phalaris, 277. 
Phallus, 245. 
Phleospora, 380. 
Phleum, 277, 278, 341. 
Phloem-necrosis, 233. 
Phlox, 407, 408, 429. 
Pholiota, 367. 
Phoma, 20, 163, 230, 369, 380, 385. 

apiicola, 178. 

betse, 162. 

cyclamense, 421. 

cydonise, 72. 

dahhse, 421. 

destructive, 263. 

lingam, 169. 

persicae, 96. 

pomi, 57. 

root-rot, 162. 

rot, 173. 
Phomopsis, 158, 250, 432. 

citri, 144. 

ka'mise, 425. 

maH, 57. 

vexans, 192, 421. 



Phoradendron, 375, 376. 
Phragmidium, subcorticum, 432. 
Phyllachora, 295, 338. 

pose, 339. 

trifoiii, 338. 
Phyllosticta, 217, 298, 369, 380, 390, 
439. 

acericola, 392. 

althaeina, 424. 

antirrhini, 434. 

apii, 178. 

batatas, 250. 

carj^ae, 395. 

catalpse, 382. 

chenopodii, 244. 

chrysanthemi, 418. 

circumscissa, 96. 

cucurbitacearum, 190. 

hydrangeae, 425. 

leaf-spot, 337. 

maculicola, 422. 

primulicola, 429. 

prunicola, 56. 

pteridis, 422. 

richardiae, 413. 

shot-hole, 74, 96. 

solitaria, 37. 

straminella, 241. 

violae, 437. 
Phymatotrichum omnivorum, 2."^. 
PhysaUs, 407. 
Physalospora, 134, 369. 

cydonise, 42, 69, 72. 
Physaruni cinereum, 408. 
Physoderma zeae-maydis, 292. 
Physopella fici, 145, 394. 
Phytophthora, 20, 135. 

cactorum, 57, 194. 

infestans, 217, 263. 

omnivorum, 26. 

phaseoli, 158. 

terrestria, 143, 265. 
Pietin, 317. 
Piggotia, 380. 
Pine, 11, 22, 117, 365, 367, 368. 369, 

371, 373, 380, 381, 395. 
Pineapple, 148. 
Pineapple-disease, 245. 
Pink, 23, 163, 429. 
Pink-disease, 135. 
Pink-mold. 395. 



502 



Index 



Pink-rot, 49, 69, 210. 
Pip, 304. 
Piped rot, 361. 
Piqueria, 407. 
Piricularia grisea, 295. 

oryzae, 300, 339. 
Pithiness, 178. 
Plantain, 135. 

Plasmodiophora brassiese, 168. 
Plasmopara viticola, 125. 
Platycodon, 407. 
Plectodiscella veneta, 102. 
Plenodomus canker, 57. 

destruens, 248. 

fuscomaculans, 57. 
Pleospora gramineum, 282. 

pisi, 213. 

tropoeoli, 427. 
Pleurotus, 367. 
Pleuteus, 367. 

Plum, 87, 88, 90, 96, 97, 98, 367. 
Poa, 278, 338. 
Pod black-rot, 135. 
Pod-blight, 158. 
Pod-rot, 157. 
Pod-spot, 152, 201. 
Podosphsera leucotrichia, 50. 

oxyacanthae, 51, 77, 91. 
Pole-rot, 259. 
Pollen-blight, 395. 
Polyporus, 361, 367. 

betulinus, 382. 

obtusus, 362. 

pergamenus, 379. 

roseus, 384. 

schweinitzii, 371. 

squamosus, 364. 

sulphureus, 361. 

versicolor, 374, 382. 
Polystictus, 368. 
Polythrincium, 328. 
Pomaceous fruits, 31, 368, 369. 
Poplar, 88, 359, 365, 367, 368, 369, 

371, 380, 381, 401. 
Poria, 368, 402. 
Portulaca, 407. 
Potassium sulfide, 448. 
Potato, 10, 22, 23, 24, 25, 26, 87, 

163, 217. 
Potato spraying, 236. 

seed disinfection, 240. 



Potentilla, 407. 
Powdery gray-rot, 420. 
Powdery -mildew, 50, 67, 77, 91, 
101, 117, 122, 134, 159, 165, 
173, 187, 195, 213, 241, 242. 
283, 300, 307, 317, 337, 338, 
342, 376, 381, 394, 407, 412, 
420, 421, 426, 429, 431, 435, 
436, 439. 
Powdery scab, 224. 
Power sprayer, 456. 
Prevention of plant diseases, 12, 13. 

methods, 14. 

historical, 3, 13. 
Primrose, 429. 
Primula, 407. 
Privet, 408, 430. 
Proprietary fungicides, 449. 
Prothallium-blight, 422. 
Protocoronospora nigricans, 338. 
Prune, 87. 
Prunus, 23, 369. 
Pseudomonas, 199, 294, 408, 422. 

angulatum, 257. 

aptatum, 164, 427. 

avense, 299. 

campestris, 165. 

citri, 137. 

erodii, 422. 

glycineum, 337. 

juglandis, 404. 

lachrymans, 185. 

maculicolum, 173. 

malvacearum, 349. 

medicaginis, 324. 

phaseoli, 155. 

pisi, 213. 

pruni, 74, 79, 90, 101. 

savastanoi, 147. 

solanacearum, 159, 174, 192, 230, 
253, 260. 

stewarti, 291. 

tabacum, 257. 

translucens, 282, 319. 

tumefaciens, 87, 104, 350, 369, 
420. 

woodsii, 416. 
Pseudopeziza medicaginis, 321. 

ribis, 115. 

trifolii, 331. 
Pseudotsuga, 368, 373. 



Index 



503 



Puccinia allii, 210. 

antirrhini, 434. 

arenarise, 429. 

asparagi, 149. 

bullata, 178. 

cannae, 413. 

chrysanthemi, 418. 

coronata, 278, 298, 339. 

dispersa, 278, 305. 

fraxinata, 381. 

glumarum, 278, 313. 

graminis, 282, 310, 339, 411. 
agrostis, 278, 340. 
airae, 278. 
avenae, 277, 298. 
phleipratensis, 278, 341. 
pose, 278. 
secalis, 277, 305. 
tritici, 277. 
tritici-compacti, 278. 

helianthi, 435. 

malvacearum, 423. 

menthse, 411. 

poarum, 338. 

porri, 210. 

pringsheimiana, 119. 

purpurea, 278. 

simplex, 278, 282. 

sorghi, 294. 

tragopogonis, 242. 

triticina, 278, 312. 

vincse, 436. 

violse, 437. 
Puccinastrum hydrangese, 425. 
Pumpkin, 22, 24, 178. 
Punica, 407. 
Pustular-spot, 95. 
Pyrenopeziza medicaginis, 322. 
Pyrethrum, 88, 407. 
Pythiacystis citriophthora, 13-5. 
Pythium, 163, 376. 

debaryanum, 193, 234, 328, .349. 

Quackgrass, 340. 

Quercus, 363. 

Quince, 23, 69, 88, 369. 

Radish, 22, 88, 163, 165. 
Ramularia, 132, 194, 380. 

armoracise, 196. 

primulae, 429. 



Rape, 163, 165. 

Raspberry, 22, 87, 88, 102. 

Rathay's disease, 339. 

Ray-blight, 419. 

Razoumofskya, 375, 376, 390. 

Red-brown root-rot, 371. 

Red-brown rot, 365. 

Red-bud, 379. 

Red cedar, 40. 

Red heart-rot, 358, 361. 

Red-leaf, 69. 

Red leaf-bhght, 350. 

Red-rot, 214, 244, 371, 384, 401. 

Red-rust, 251. 

Redtop, 280, 340. 

Reseda, 407. 

Rhabdospora, 145. 

Rhamnus cathartica, 298. 
lanceolatus, 298. 

Rheosporangium aphanidermaius, 
163. 

Rhino trichum, 346. 

Rhizina, 373. 

Rhizoctonia, 21, 178, 225, 328, 33 
349. 
crocorum, 327. 
leaf-blight, 146. 

Rhizopus, 57. 

nigricans, 134, 191, 234, 245, 264. 

Rhododendron, 408. 
viscosum, 113. 

Rhubarb, 22, 23, 241. 

Rhytisma, 380. 
acerinum, 392. 
punctatum, 392. 

Rice, 300. 

Richardia, 407. 

Ricinus, 407. 

Rind-disease, 245. 

Ring-spot, 173, 245. 

Ripe-rot, 146. 

Roestelia, 39, 67, 69. 

Root-knot, 24, 146, 159, 162, 169, 
191, 193, 195, 200, 213, 217, 
251, 259, 265, 335, 348. 

Root-rot, 21, 23, 24, 51, 117, 119, 
130, 143, 145, 146, 162, 191, 196, 
213, 245, 248, 289, 325, 327, 331, 
337, 370, 402, 405, 408, 421, 
435, 437, 439. 

Root-tumor, 164. 



,, N 



f.04 



Index 



Rose, 24, 87, 367, 407, 408, 430. 

Rose-of-Sharon, 423. 

Roselle, 94, 241, 265. 

Rosette, 57, 101, 198, 395. 

Rot, 111, 135, 148. 194, 365, 417, 
420. (See also boll-rot, brown- 
rot, blossom-rot, gray-rot, soft- 
rot, root-rot, ripe-rot, bitter- 
rot, black-rot, pink-rot, red- 
rot, pod-rot, white-rot, stem- 
rot, wood-rot, root-rot, timber- 
rot.) 

Rotten-neck, 300. 

Rough -bark, 57. 

Rubber, 402. 

Rust, 39, 67, 69, 74, 79, 96, 101, 116, 
144, 145, 149, 154, 164, 178, 
196, 210, 213, 214, 242, 251, 
275, 282, 294, 304, 328, 329, 
338, 341, 349, 352, 380, 381, 
382, 383, 390, 394, 400, 401, 
405, 409, 410, 411, 413, 414, 
418, 420, 423, 425, 427, 428, 
429, 432, 434, 435, 436, 437. 
(See also black-rust, blister- 
rust, black-stem-rust, white- 
rust, late-rust, orange-rust, 
yellow-rust.) 

Rutaba<?a, 163, 165. 

Rye, 163, 280, 304. 

Salsify, 25, 88, 241. 
Salvia, 407. 
Santolina, 407. 
Sap-rot, 374. 
Sapwood rot, 364, 382. 
Sargent sterilizer, 462. 
Sassafras, 367, 402. 
Scab, 27, 35, 68, 74, 79. 82, 99, 132, 
142, 147, 163, 178, 283, 298, 307, 
318, 331, 394. 
Scald, 54, 110. 
Scaly-bark, 140. 
Schizanthus, 407. 
Schizophyllum, 346, 368. 

alneum, 78. 
Sclerospora, 295. 

Sclerotinia, 20, 164, 174, 178, 265, 
426, 429, 435. 

cinerea, 55, 75, 79, 101 . 

fuckeliana, 132. 



libertiana, 26, 137, 158, 170, 183, 
193, 195, 196, 258. 

linhartiana, 73. 

oxycocci, 112. 

perplexa, 435. 

smilacina, 194. 

trifoliorum, 323, 329. 

tuberosa, 409. 

white rot, 195. 
Sclerotium, 20, 174, 193, 242, 320, 
346. 

bataticola, 218, 251. 

ricini, 174. 

rolfsii, 23, 144, 146, 158, 185, 195, 
214, 215, 264, 408, 420. 
Scolecotrichum graminis, 339. 
Scurf, 56, 250. 
Secale, 277, 278. 
Sedum, 407, 433. 
Seed-bed diseases, 407. 
Seed mold, 328. 
Seed plat, 275. 
Septobasidium, 53, 368, 372. 

canker, 57, 69. 

pedicillatum, 57. 
Septocylindrium rufomaculans, 165. 

areola, 348. 
Septogloeum, 380. 
Septoria, 68, 114, 328, 381, 411, 424. 

armoracese, 195. 

bataticola, 251. 

chrysanthemella, 418. 

consimilis, 199. 

dianthi, 415. 

gladioli, 423. 

helianthi, 435. 

kalmicola, 425. 

lactucae, 199. 

leaf-spot, 191, 337. 

lycopersici, 262. 

petroselini, 174. 

ricini, 174. 

rubi, 104. 

sedi, 433. 
Sequoia, 379, 381. 
Seradella, 407. 
Shadbush, 380, 381. 
Shedding, 350. 
Sheep laurel, 113. 
Shelling, 131. 
Shoe-string root-rot, 370. 



Index 



505 \<)i 



Shot-hole, 74, 96. 
Sida, 23. 
Silene, 407. 

Silver-leaf, 74. 96, 99, 117. 
Silver-scurf, 234. 
Slime flux, 376. 
Slime-mold, 408. 
Slimy-rot, 114. 
Small fruits, 102. 

Smut, 26, 201. 266, 283, 295. -338, 
339, 340, 341, 349, 411. (See 
also covered-smut, kernel-smut, 
loose-smut, black-smut, cereal- 
smut.) 

kinds of, 266. 

preventive treatments. 268. 

seed treatments, 270. 
Snap dragon, 434. 
Soft-gall, 88. 
Soft heart-rot. 382. 
Soft-rot, 26, 51. 164, 172, 179, 188, 
194, 208, 217, 241, 245, 362, 
412, 420. 
Soil diseases, 26. 
Soil-disinfection. 460. 
Soil-rot, 249. 
Sooty-blotch, 55, 69. 
Sooty-mold, 144, 265, 408. 413. 
Sore-shin, 349. 
Sorghum, 163, 278, 307. 
Sour-rot, 144. 

Southern-blight, 23, 146. 158. 174, 
185, 193, 195, 214, 215, 242, 
264, 320, 408. 420. 
Soy bean, 24. 337. 
Sparassis, 373. 
Spartina. 381. 
Speck, 304. 
Spelt, 310. 
Sphacelotheca reiliana, 286, 309. 

cruenta, 308. 

sorghi, 283, 308. 
Sphaeronema fimbriatum. 247. 
Sphseronemella, 134. 
Sphaeropsis malorum, 42. 69, 72, 
.369. 

tumefaciens, 144. 

vincae, 436. 
Sphaerotheca humuli. 1.34. 195. 431. 

mors-uvae. 117. 

pannosa, 91, 431. 



Spinach, 25, 163, 242. 

Spindling-sprout, 235. 

Spirea, 407. ^ 

Spondylocladium atrovirens, 234. 

Spongospora subterranea, 224, 

Sporobolus, 277. 

Sporonema. 323. 

Sporotrichum anthophilum, 417. 

Spot, 201, 257, 336. (See also leaf- 
spot, angular leaf -spot, black- 
spot, pod-spot.) 

Spot-disease, 436. 

Spotted blight, 304. 

Spray gun, 456. 

Spraying, 191. 

Spraying apparatus, 452. 

Spraying schedule, conditions in- 
fluencing, for apples, 57. 

Spur-blight. 107. 

Spruce, 365, 367, 368, 369, 371, 373, 
380. 

Spurge, 435. 

Squash, 22, 23, 178. 

Stachys, 407. 

Stagonospora carpathica, 328. 
leaf-spot, 328. 

Stalk-rot, 289. 

Steccherinum, 368. 

Stem anthracnose, 193. 

blight, 96, 421. C 

disease. 145. 

Stem-end-rot, 144, 187. 

Stem-rot, 21, 157, 213, 249, 259, 407, 
410, 416, 417, 420, 439. 

Stem-smut, 306. 

Stemphylium cucurbitacearum, 190. 

Stereum, 368. 
purpureum, 99. 

Sterigmatocystis nigra, 146, 210, 
260. 

Stigmatea. 381. 

Stigmonose, 416. 

Stilbella flavida, 145. 

Stilbum, 251. 

Stinking-smut. 314. 

Stocks, 168. 

Strawberry, 25, 132. 

Streak, 159. 435. 437. 

Stripe-bHght. 299. 307, 342. 

Stripe-disease, 282, 307. 

Strophostyles, 155. 

Strumella, 369. 



506 



Index 



Sudan-grass, 307. 

Sugar-beet, 24. 

Sugar-cane, 23, 24, 244. 

Sulfur-dust, 446. 

Sun-burn, 40.5. 

Sunflower, 163, 407, 435. 

Sunscald, 54, 159. 

Sweet-alyssum, 168. 

Sweet-gum, 381. 

Sweet-pea, 24, 163, 407, 408, 435. 

Sweet potato, 22, 23, 24, 26, 245. 

Sycamore, 367, 369, 371, 380, 381, 

403. 
Synchytrium endobioticum, 224. 
vaccinii, 113. 

Take-all, 317. 
Tall oat grass, 340. 
Taphrina, 376. 381. 

cerasi, 77. 

coerulescens, 394. 

communis, 98. 

deformans, 84. 
Tar-spot, 392. 
Taxus, 407. 
Tea, 251. 
Telanthera, 407. 
Teosinte, 283. 
Texas root-rot, 23, 53, 69, 201, 248, 

323, 346. 
Thelephora, 368. 
Thielavia, 191, 196, 213. 

basicola, 24, 194, 251, .337, 373, 
408, 421, 435. 

root-rot, 194. 
Thielaviopsis paradoxa, 148, 245. 
Thread-blight, 251. 
Thrombosis, .393. 
Thyridaria, 402. 
Tilletia horrida. 302. 

laevis, 314. 

tritioi, 314. 
Timber, 354, 373. 
Timber-rot, 183, 265. 
Timothy, 163, 280, 341. 
Tip-burn, 228. 
Tobacco, 22, 25, 87, 251. 
Tomato, 22, 23, 25, 87, 260. 
Tower, 458. 
Trametes, 368. 

pini, 358. 



Transchelia, 423. 

punctata, 96. 
Trees, 354. 
Tree surgery, 376. 
Trichoderma koningi, 251. 

-rot, 251. 
Tricholoma, 368, 372. 
Trichosphaeria, 148. 

sacchari, 245. 
Triticum, 277, 278. 
Tropical fruits, 135. 
Tropoeolum, 408, 427. 
Tsuga heterophylla, 389. 
Tubercularia, 146. 
Tulip, 369, 436. 
Tupelo, 368. 
Turnip, 88, 163, 165. 
Tussilago, 338. 
Twig-blight, 368, 394, 398. 

Uncinula necator, 122. 
Uredinales, 380. 
Uredo, 148. 

arachidis, 214. 
Urocystis agropyri, 340. 

cepulse, 201. 

occulta, 306. 
Uromyces, 148, 329, 338. 

appendiculatus, 154. 

betffi, 164. 

caryophyllinus, 414. 

pose, 339. 

striatus, 328. 
Urophlyctis, 164. 

alfalfa?, 325. 

tritici, 316. 
Ustilaginoidea virens, 301o 
Ustilago, 295, 340. 

avense, 296. 

crameri, 295. 

crusgalli, 338. 

hordei, 282. 

levis, 297. 

nuda, 280. 

panici-miliacei, 295. 

perennans, 340. 

shiraiana, 411. 

striajformis, 338, 340, 341. 

tritici, 315. 

zeae, 283. 



Index 



507 



Valsa, 369. 

leucostoma, 74, 78, 86. 
Vanilla, 148. 
Vegetable crops, 149. 
Venturia, 381. 

inaequalis, 35. 

pyrina, 68. 
Verbena, 407, 436. 
Vermicularia, 148, 208. 

dematium, 193. 

subeffigurata, 415. 

telephii, 433. 

trichella, 425. 
Verticillium, 192, 393. 

alboatrum, 201, 230, 412. 

albus, 194. 

caulophagus, 110. 

dahlise, 421. 

wilt, 194. 
Vetch, 24, 163, 338. 
Vigna, 155. 
Vinca, 407. 
Vinca leaf-spot, 436. 
Viola, 407. 

Violet, 22, 23, 24, 408, 436. 
Virginia creeper, 407, 439. 
Viruela, 145. 
Volutella, 20, 205, 346. 

concentrica, 412. 

dianthi, 417. 

fructi, 56. 

rot, 56, 412. 
Volvaria, 368. 

Walnut, 25, 87, 359, 361, 364, 
367, 368, 369, 379, 380, 381, 
403- 
Wart, 224. 
Water lily, 439. 
Watermelon, 22, 23, 26, 178. 
Watery -rot, 144. 



Wet-butts, 260. 

Wheat, 163, 280, 310. 

White alder, 113. 

White cedar, 368, 369. 

White-head, 317. 

White heart-rot, 359. 

White-rot, 132, 361, 364, 381, 383. 

White rust, 164, 172, 173, 196, 
241, 250, 408, 427. 

White-smut, 242. 

White-spot, 328. 

White- vein, 260. 

White wood-rot, 364. 

Wildfire, 257. 

Willow, 25, 88, 359, 364, 367, 368, 
.369, 376, 379, 380, 381, 405. 

Wilt, 26, 98, 112, 135, 148, 159. 
172, 174, 181, 182, 190, 192, 
193, 201, 213, 215, 228, 230. 
249, 257, 260, 291. 323, 325, 
329, 331, 337, 343, 350, 353, 
409, 412, 416, 418, 421, 435, 437. 

Winter-blight, 265. 

Wintergreen , 113. 

Witches-broom, 135. 

Wither-tip, 143. 

Wood-rot, 53, 78, 144. 

Xylaria, 53, 373. 

Yellow leaf, 294, 300. 

Yellow leaf-blotch, 322. 

Yellow-rust, 146. 

Yellow-stripe rust, 283, 307, 313. 

Yellow-top, 328. 

Yellow wood-rot, 391. 

Yellows, 74, 79, 91, 101, 108, 172, 

405, 410, 417. 
Yew, 408. 

Zygodesmus albidus, 439. 



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